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  1. 21 1月, 2019 1 次提交
    • P
      futex: Fix (possible) missed wakeup · b061c38b
      由 Peter Zijlstra 提交于 
      We must not rely on wake_q_add() to delay the wakeup; in particular
commit:

  1d0dcb3a ("futex: Implement lockless wakeups")

moved wake_q_add() before smp_store_release(&q->lock_ptr, NULL), which
could result in futex_wait() waking before observing ->lock_ptr ==
NULL and going back to sleep again.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1d0dcb3a ("futex: Implement lockless wakeups")
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      b061c38b
  3. 04 1月, 2019 1 次提交
    • L
      Remove 'type' argument from access_ok() function · 96d4f267
      由 Linus Torvalds 提交于 
      Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
of the user address range verification function since we got rid of the
old racy i386-only code to walk page tables by hand.

It existed because the original 80386 would not honor the write protect
bit when in kernel mode, so you had to do COW by hand before doing any
user access.  But we haven't supported that in a long time, and these
days the 'type' argument is a purely historical artifact.

A discussion about extending 'user_access_begin()' to do the range
checking resulted this patch, because there is no way we're going to
move the old VERIFY_xyz interface to that model.  And it's best done at
the end of the merge window when I've done most of my merges, so let's
just get this done once and for all.

This patch was mostly done with a sed-script, with manual fix-ups for
the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.

There were a couple of notable cases:

 - csky still had the old "verify_area()" name as an alias.

 - the iter_iov code had magical hardcoded knowledge of the actual
   values of VERIFY_{READ,WRITE} (not that they mattered, since nothing
   really used it)

 - microblaze used the type argument for a debug printout

but other than those oddities this should be a total no-op patch.

I tried to fix up all architectures, did fairly extensive grepping for
access_ok() uses, and the changes are trivial, but I may have missed
something.  Any missed conversion should be trivially fixable, though.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      96d4f267
  5. 19 12月, 2018 1 次提交
    • T
      futex: Cure exit race · da791a66
      由 Thomas Gleixner 提交于 
      Stefan reported, that the glibc tst-robustpi4 test case fails
occasionally. That case creates the following race between
sys_exit() and sys_futex_lock_pi():

 CPU0				CPU1

 sys_exit()			sys_futex()
  do_exit()			 futex_lock_pi()
   exit_signals(tsk)		  No waiters:
    tsk->flags |= PF_EXITING;	  *uaddr == 0x00000PID
  mm_release(tsk)		  Set waiter bit
   exit_robust_list(tsk) {	  *uaddr = 0x80000PID;
      Set owner died		  attach_to_pi_owner() {
    *uaddr = 0xC0000000;	   tsk = get_task(PID);
   }				   if (!tsk->flags & PF_EXITING) {
  ...				     attach();
  tsk->flags |= PF_EXITPIDONE;	   } else {
				     if (!(tsk->flags & PF_EXITPIDONE))
				       return -EAGAIN;
				     return -ESRCH; <--- FAIL
				   }

ESRCH is returned all the way to user space, which triggers the glibc test
case assert. Returning ESRCH unconditionally is wrong here because the user
space value has been changed by the exiting task to 0xC0000000, i.e. the
FUTEX_OWNER_DIED bit is set and the futex PID value has been cleared. This
is a valid state and the kernel has to handle it, i.e. taking the futex.

Cure it by rereading the user space value when PF_EXITING and PF_EXITPIDONE
is set in the task which 'owns' the futex. If the value has changed, let
the kernel retry the operation, which includes all regular sanity checks
and correctly handles the FUTEX_OWNER_DIED case.

If it hasn't changed, then return ESRCH as there is no way to distinguish
this case from malfunctioning user space. This happens when the exiting
task did not have a robust list, the robust list was corrupted or the user
space value in the futex was simply bogus.
Reported-by: NStefan Liebler <stli@linux.ibm.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=200467
Link: https://lkml.kernel.org/r/20181210152311.986181245@linutronix.de
      da791a66
  7. 08 12月, 2018 2 次提交
    • A
      y2038: futex: Add support for __kernel_timespec · bec2f7cb
      由 Arnd Bergmann 提交于 
      This prepares sys_futex for y2038 safe calling: the native
syscall is changed to receive a __kernel_timespec argument, which
will be switched to 64-bit time_t in the future. All the internal
time handling gets changed to timespec64, and the compat_sys_futex
entry point is moved under the CONFIG_COMPAT_32BIT_TIME check
to provide compatibility for existing 32-bit architectures.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
      bec2f7cb
    • A
      y2038: futex: Move compat implementation into futex.c · 04e7712f
      由 Arnd Bergmann 提交于 
      We are going to share the compat_sys_futex() handler between 64-bit
architectures and 32-bit architectures that need to deal with both 32-bit
and 64-bit time_t, and this is easier if both entry points are in the
same file.

In fact, most other system call handlers do the same thing these days, so
let's follow the trend here and merge all of futex_compat.c into futex.c.

In the process, a few minor changes have to be done to make sure everything
still makes sense: handle_futex_death() and futex_cmpxchg_enabled() become
local symbol, and the compat version of the fetch_robust_entry() function
gets renamed to compat_fetch_robust_entry() to avoid a symbol clash.

This is intended as a purely cosmetic patch, no behavior should
change.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
      04e7712f
  9. 31 10月, 2018 1 次提交
  11. 09 10月, 2018 1 次提交
  13. 21 8月, 2018 1 次提交
  15. 07 2月, 2018 1 次提交
  17. 24 1月, 2018 1 次提交
  19. 15 1月, 2018 2 次提交
    • L
      futex: Prevent overflow by strengthen input validation · fbe0e839
      由 Li Jinyue 提交于 
      UBSAN reports signed integer overflow in kernel/futex.c:

 UBSAN: Undefined behaviour in kernel/futex.c:2041:18
 signed integer overflow:
 0 - -2147483648 cannot be represented in type 'int'

Add a sanity check to catch negative values of nr_wake and nr_requeue.
Signed-off-by: NLi Jinyue <lijinyue@huawei.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: dvhart@infradead.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1513242294-31786-1-git-send-email-lijinyue@huawei.com
      fbe0e839
    • P
      futex: Avoid violating the 10th rule of futex · c1e2f0ea
      由 Peter Zijlstra 提交于 
      Julia reported futex state corruption in the following scenario:

   waiter                                  waker                                            stealer (prio > waiter)

   futex(WAIT_REQUEUE_PI, uaddr, uaddr2,
         timeout=[N ms])
      futex_wait_requeue_pi()
         futex_wait_queue_me()
            freezable_schedule()
            <scheduled out>
                                           futex(LOCK_PI, uaddr2)
                                           futex(CMP_REQUEUE_PI, uaddr,
                                                 uaddr2, 1, 0)
                                              /* requeues waiter to uaddr2 */
                                           futex(UNLOCK_PI, uaddr2)
                                                 wake_futex_pi()
                                                    cmp_futex_value_locked(uaddr2, waiter)
                                                    wake_up_q()
           <woken by waker>
           <hrtimer_wakeup() fires,
            clears sleeper->task>
                                                                                           futex(LOCK_PI, uaddr2)
                                                                                              __rt_mutex_start_proxy_lock()
                                                                                                 try_to_take_rt_mutex() /* steals lock */
                                                                                                    rt_mutex_set_owner(lock, stealer)
                                                                                              <preempted>
         <scheduled in>
         rt_mutex_wait_proxy_lock()
            __rt_mutex_slowlock()
               try_to_take_rt_mutex() /* fails, lock held by stealer */
               if (timeout && !timeout->task)
                  return -ETIMEDOUT;
            fixup_owner()
               /* lock wasn't acquired, so,
                  fixup_pi_state_owner skipped */

   return -ETIMEDOUT;

   /* At this point, we've returned -ETIMEDOUT to userspace, but the
    * futex word shows waiter to be the owner, and the pi_mutex has
    * stealer as the owner */

   futex_lock(LOCK_PI, uaddr2)
     -> bails with EDEADLK, futex word says we're owner.

And suggested that what commit:

  73d786bd ("futex: Rework inconsistent rt_mutex/futex_q state")

removes from fixup_owner() looks to be just what is needed. And indeed
it is -- I completely missed that requeue_pi could also result in this
case. So we need to restore that, except that subsequent patches, like
commit:

  16ffa12d ("futex: Pull rt_mutex_futex_unlock() out from under hb->lock")

changed all the locking rules. Even without that, the sequence:

-               if (rt_mutex_futex_trylock(&q->pi_state->pi_mutex)) {
-                       locked = 1;
-                       goto out;
-               }

-               raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
-               owner = rt_mutex_owner(&q->pi_state->pi_mutex);
-               if (!owner)
-                       owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
-               raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
-               ret = fixup_pi_state_owner(uaddr, q, owner);

already suggests there were races; otherwise we'd never have to look
at next_owner.

So instead of doing 3 consecutive wait_lock sections with who knows
what races, we do it all in a single section. Additionally, the usage
of pi_state->owner in fixup_owner() was only safe because only the
rt_mutex owner would modify it, which this additional case wrecks.

Luckily the values can only change away and not to the value we're
testing, this means we can do a speculative test and double check once
we have the wait_lock.

Fixes: 73d786bd ("futex: Rework inconsistent rt_mutex/futex_q state")
Reported-by: NJulia Cartwright <julia@ni.com>
Reported-by: NGratian Crisan <gratian.crisan@ni.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NJulia Cartwright <julia@ni.com>
Tested-by: NGratian Crisan <gratian.crisan@ni.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171208124939.7livp7no2ov65rrc@hirez.programming.kicks-ass.net
      c1e2f0ea
  21. 11 12月, 2017 1 次提交
  23. 02 11月, 2017 1 次提交
    • J
      futex: futex_wake_op, do not fail on invalid op · e78c38f6
      由 Jiri Slaby 提交于 
      In commit 30d6e0a4 ("futex: Remove duplicated code and fix undefined
behaviour"), I let FUTEX_WAKE_OP to fail on invalid op.  Namely when op
should be considered as shift and the shift is out of range (< 0 or > 31).

But strace's test suite does this madness:

  futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xa0caffee);
  futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xbadfaced);
  futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xffffffff);

When I pick the first 0xa0caffee, it decodes as:

  0x80000000 & 0xa0caffee: oparg is shift
  0x70000000 & 0xa0caffee: op is FUTEX_OP_OR
  0x0f000000 & 0xa0caffee: cmp is FUTEX_OP_CMP_EQ
  0x00fff000 & 0xa0caffee: oparg is sign-extended 0xcaf = -849
  0x00000fff & 0xa0caffee: cmparg is sign-extended 0xfee = -18

That means the op tries to do this:

  (futex |= (1 << (-849))) == -18

which is completely bogus. The new check of op in the code is:

        if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
                if (oparg < 0 || oparg > 31)
                        return -EINVAL;
                oparg = 1 << oparg;
        }

which results obviously in the "Invalid argument" errno:

  FAIL: futex
  ===========

  futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xa0caffee) = -1: Invalid argument
  futex.test: failed test: ../futex failed with code 1

So let us soften the failure to print only a (ratelimited) message, crop
the value and continue as if it were right.  When userspace keeps up, we
can switch this to return -EINVAL again.

[v2] Do not return 0 immediatelly, proceed with the cropped value.

Fixes: 30d6e0a4 ("futex: Remove duplicated code and fix undefined behaviour")
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e78c38f6
  25. 01 11月, 2017 1 次提交
    • P
      futex: Fix more put_pi_state() vs. exit_pi_state_list() races · 153fbd12
      由 Peter Zijlstra 提交于 
      Dmitry (through syzbot) reported being able to trigger the WARN in
get_pi_state() and a use-after-free on:

	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);

Both are due to this race:

  exit_pi_state_list()				put_pi_state()

  lock(&curr->pi_lock)
  while() {
	pi_state = list_first_entry(head);
	hb = hash_futex(&pi_state->key);
	unlock(&curr->pi_lock);

						dec_and_test(&pi_state->refcount);

	lock(&hb->lock)
	lock(&pi_state->pi_mutex.wait_lock)	// uaf if pi_state free'd
	lock(&curr->pi_lock);

	....

	unlock(&curr->pi_lock);
	get_pi_state();				// WARN; refcount==0

The problem is we take the reference count too late, and don't allow it
being 0. Fix it by using inc_not_zero() and simply retrying the loop
when we fail to get a refcount. In that case put_pi_state() should
remove the entry from the list.
Reported-by: NDmitry Vyukov <dvyukov@google.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Gratian Crisan <gratian.crisan@ni.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: dvhart@infradead.org
Cc: syzbot <bot+2af19c9e1ffe4d4ee1d16c56ae7580feaee75765@syzkaller.appspotmail.com>
Cc: syzkaller-bugs@googlegroups.com
Cc: <stable@vger.kernel.org>
Fixes: c74aef2d ("futex: Fix pi_state->owner serialization")
Link: http://lkml.kernel.org/r/20171031101853.xpfh72y643kdfhjs@hirez.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      153fbd12
  27. 25 9月, 2017 1 次提交
  29. 26 8月, 2017 1 次提交
    • J
      futex: Remove duplicated code and fix undefined behaviour · 30d6e0a4
      由 Jiri Slaby 提交于 
      There is code duplicated over all architecture's headers for
futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
and comparison of the result.

Remove this duplication and leave up to the arches only the needed
assembly which is now in arch_futex_atomic_op_inuser.

This effectively distributes the Will Deacon's arm64 fix for undefined
behaviour reported by UBSAN to all architectures. The fix was done in
commit 5f16a046 (arm64: futex: Fix undefined behaviour with
FUTEX_OP_OPARG_SHIFT usage). Look there for an example dump.

And as suggested by Thomas, check for negative oparg too, because it was
also reported to cause undefined behaviour report.

Note that s390 removed access_ok check in d12a2970 ("s390/uaccess:
remove pointless access_ok() checks") as access_ok there returns true.
We introduce it back to the helper for the sake of simplicity (it gets
optimized away anyway).
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NRussell King <rmk+kernel@armlinux.org.uk>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> [s390]
Acked-by: Chris Metcalf <cmetcalf@mellanox.com> [for tile]
Reviewed-by: NDarren Hart (VMware) <dvhart@infradead.org>
Reviewed-by: Will Deacon <will.deacon@arm.com> [core/arm64]
Cc: linux-mips@linux-mips.org
Cc: Rich Felker <dalias@libc.org>
Cc: linux-ia64@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: peterz@infradead.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: sparclinux@vger.kernel.org
Cc: Jonas Bonn <jonas@southpole.se>
Cc: linux-s390@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: linux-hexagon@vger.kernel.org
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-snps-arc@lists.infradead.org
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-xtensa@linux-xtensa.org
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: openrisc@lists.librecores.org
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Stafford Horne <shorne@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Richard Henderson <rth@twiddle.net>
Cc: Chris Zankel <chris@zankel.net>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-parisc@vger.kernel.org
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: linux-alpha@vger.kernel.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: "David S. Miller" <davem@davemloft.net>
Link: http://lkml.kernel.org/r/20170824073105.3901-1-jslaby@suse.cz
      30d6e0a4
  31. 10 8月, 2017 1 次提交
    • M
      futex: Remove unnecessary warning from get_futex_key · 48fb6f4d
      由 Mel Gorman 提交于 
      Commit 65d8fc77 ("futex: Remove requirement for lock_page() in
get_futex_key()") removed an unnecessary lock_page() with the
side-effect that page->mapping needed to be treated very carefully.

Two defensive warnings were added in case any assumption was missed and
the first warning assumed a correct application would not alter a
mapping backing a futex key.  Since merging, it has not triggered for
any unexpected case but Mark Rutland reported the following bug
triggering due to the first warning.

  kernel BUG at kernel/futex.c:679!
  Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 0 PID: 3695 Comm: syz-executor1 Not tainted 4.13.0-rc3-00020-g307fec773ba3 #3
  Hardware name: linux,dummy-virt (DT)
  task: ffff80001e271780 task.stack: ffff000010908000
  PC is at get_futex_key+0x6a4/0xcf0 kernel/futex.c:679
  LR is at get_futex_key+0x6a4/0xcf0 kernel/futex.c:679
  pc : [<ffff00000821ac14>] lr : [<ffff00000821ac14>] pstate: 80000145

The fact that it's a bug instead of a warning was due to an unrelated
arm64 problem, but the warning itself triggered because the underlying
mapping changed.

This is an application issue but from a kernel perspective it's a
recoverable situation and the warning is unnecessary so this patch
removes the warning.  The warning may potentially be triggered with the
following test program from Mark although it may be necessary to adjust
NR_FUTEX_THREADS to be a value smaller than the number of CPUs in the
system.

    #include <linux/futex.h>
    #include <pthread.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/mman.h>
    #include <sys/syscall.h>
    #include <sys/time.h>
    #include <unistd.h>

    #define NR_FUTEX_THREADS 16
    pthread_t threads[NR_FUTEX_THREADS];

    void *mem;

    #define MEM_PROT  (PROT_READ | PROT_WRITE)
    #define MEM_SIZE  65536

    static int futex_wrapper(int *uaddr, int op, int val,
                             const struct timespec *timeout,
                             int *uaddr2, int val3)
    {
        syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
    }

    void *poll_futex(void *unused)
    {
        for (;;) {
            futex_wrapper(mem, FUTEX_CMP_REQUEUE_PI, 1, NULL, mem + 4, 1);
        }
    }

    int main(int argc, char *argv[])
    {
        int i;

        mem = mmap(NULL, MEM_SIZE, MEM_PROT,
               MAP_SHARED | MAP_ANONYMOUS, -1, 0);

        printf("Mapping @ %p\n", mem);

        printf("Creating futex threads...\n");

        for (i = 0; i < NR_FUTEX_THREADS; i++)
            pthread_create(&threads[i], NULL, poll_futex, NULL);

        printf("Flipping mapping...\n");
        for (;;) {
            mmap(mem, MEM_SIZE, MEM_PROT,
                 MAP_FIXED | MAP_SHARED | MAP_ANONYMOUS, -1, 0);
        }

        return 0;
    }
Reported-and-tested-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NMel Gorman <mgorman@suse.de>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org # 4.7+
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      48fb6f4d
  33. 01 8月, 2017 1 次提交
  35. 01 7月, 2017 1 次提交
    • K
      randstruct: Mark various structs for randomization · 3859a271
      由 Kees Cook 提交于 
      This marks many critical kernel structures for randomization. These are
structures that have been targeted in the past in security exploits, or
contain functions pointers, pointers to function pointer tables, lists,
workqueues, ref-counters, credentials, permissions, or are otherwise
sensitive. This initial list was extracted from Brad Spengler/PaX Team's
code in the last public patch of grsecurity/PaX based on my understanding
of the code. Changes or omissions from the original code are mine and
don't reflect the original grsecurity/PaX code.

Left out of this list is task_struct, which requires special handling
and will be covered in a subsequent patch.
Signed-off-by: NKees Cook <keescook@chromium.org>
      3859a271
  37. 20 6月, 2017 1 次提交
    • I
      sched/wait: Rename wait_queue_t => wait_queue_entry_t · ac6424b9
      由 Ingo Molnar 提交于 
      Rename:

	wait_queue_t		=>	wait_queue_entry_t

'wait_queue_t' was always a slight misnomer: its name implies that it's a "queue",
but in reality it's a queue *entry*. The 'real' queue is the wait queue head,
which had to carry the name.

Start sorting this out by renaming it to 'wait_queue_entry_t'.

This also allows the real structure name 'struct __wait_queue' to
lose its double underscore and become 'struct wait_queue_entry',
which is the more canonical nomenclature for such data types.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      ac6424b9
  39. 16 5月, 2017 1 次提交
    • M
      mutex, futex: adjust kernel-doc markups to generate ReST · 7b4ff1ad
      由 Mauro Carvalho Chehab 提交于 
      There are a few issues on some kernel-doc markups that was
causing troubles with kernel-doc output on ReST format:

./kernel/futex.c:492: WARNING: Inline emphasis start-string without end-string.
./kernel/futex.c:1264: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:1721: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2338: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2426: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2899: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2972: WARNING: Block quote ends without a blank line; unexpected unindent.

Fix them.

No functional changes.
Acked-by: NDarren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>
      7b4ff1ad
  41. 15 4月, 2017 1 次提交
  43. 14 4月, 2017 2 次提交
  45. 04 4月, 2017 2 次提交
  47. 24 3月, 2017 12 次提交
    • P
      futex: Drop hb->lock before enqueueing on the rtmutex · 56222b21
      由 Peter Zijlstra 提交于 
      When PREEMPT_RT_FULL does the spinlock -> rt_mutex substitution the PI
chain code will (falsely) report a deadlock and BUG.

The problem is that it hold hb->lock (now an rt_mutex) while doing
task_blocks_on_rt_mutex on the futex's pi_state::rtmutex. This, when
interleaved just right with futex_unlock_pi() leads it to believe to see an
AB-BA deadlock.

  Task1 (holds rt_mutex,	Task2 (does FUTEX_LOCK_PI)
         does FUTEX_UNLOCK_PI)

				lock hb->lock
				lock rt_mutex (as per start_proxy)
  lock hb->lock

Which is a trivial AB-BA.

It is not an actual deadlock, because it won't be holding hb->lock by the
time it actually blocks on the rt_mutex, but the chainwalk code doesn't
know that and it would be a nightmare to handle this gracefully.

To avoid this problem, do the same as in futex_unlock_pi() and drop
hb->lock after acquiring wait_lock. This still fully serializes against
futex_unlock_pi(), since adding to the wait_list does the very same lock
dance, and removing it holds both locks.

Aside of solving the RT problem this makes the lock and unlock mechanism
symetric and reduces the hb->lock held time.
Reported-and-tested-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Suggested-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104152.161341537@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      56222b21
    • P
      futex: Futex_unlock_pi() determinism · bebe5b51
      由 Peter Zijlstra 提交于 
      The problem with returning -EAGAIN when the waiter state mismatches is that
it becomes very hard to proof a bounded execution time on the
operation. And seeing that this is a RT operation, this is somewhat
important.

While in practise; given the previous patch; it will be very unlikely to
ever really take more than one or two rounds, proving so becomes rather
hard.

However, now that modifying wait_list is done while holding both hb->lock
and wait_lock, the scenario can be avoided entirely by acquiring wait_lock
while still holding hb-lock. Doing a hand-over, without leaving a hole.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104152.112378812@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      bebe5b51
    • P
      futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() · cfafcd11
      由 Peter Zijlstra 提交于 
      By changing futex_lock_pi() to use rt_mutex_*_proxy_lock() all wait_list
modifications are done under both hb->lock and wait_lock.

This closes the obvious interleave pattern between futex_lock_pi() and
futex_unlock_pi(), but not entirely so. See below:

Before:

futex_lock_pi()			futex_unlock_pi()
  unlock hb->lock

				  lock hb->lock
				  unlock hb->lock

				  lock rt_mutex->wait_lock
				  unlock rt_mutex_wait_lock
				    -EAGAIN

  lock rt_mutex->wait_lock
  list_add
  unlock rt_mutex->wait_lock

  schedule()

  lock rt_mutex->wait_lock
  list_del
  unlock rt_mutex->wait_lock

				  <idem>
				    -EAGAIN

  lock hb->lock


After:

futex_lock_pi()			futex_unlock_pi()

  lock hb->lock
  lock rt_mutex->wait_lock
  list_add
  unlock rt_mutex->wait_lock
  unlock hb->lock

  schedule()
				  lock hb->lock
				  unlock hb->lock
  lock hb->lock
  lock rt_mutex->wait_lock
  list_del
  unlock rt_mutex->wait_lock

				  lock rt_mutex->wait_lock
				  unlock rt_mutex_wait_lock
				    -EAGAIN

  unlock hb->lock


It does however solve the earlier starvation/live-lock scenario which got
introduced with the -EAGAIN since unlike the before scenario; where the
-EAGAIN happens while futex_unlock_pi() doesn't hold any locks; in the
after scenario it happens while futex_unlock_pi() actually holds a lock,
and then it is serialized on that lock.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104152.062785528@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      cfafcd11
    • P
      futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock() · 38d589f2
      由 Peter Zijlstra 提交于 
      With the ultimate goal of keeping rt_mutex wait_list and futex_q waiters
consistent it's necessary to split 'rt_mutex_futex_lock()' into finer
parts, such that only the actual blocking can be done without hb->lock
held.

Split split_mutex_finish_proxy_lock() into two parts, one that does the
blocking and one that does remove_waiter() when the lock acquire failed.

When the rtmutex was acquired successfully the waiter can be removed in the
acquisiton path safely, since there is no concurrency on the lock owner.

This means that, except for futex_lock_pi(), all wait_list modifications
are done with both hb->lock and wait_lock held.

[bigeasy@linutronix.de: fix for futex_requeue_pi_signal_restart]
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104152.001659630@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      38d589f2
    • P
      futex,rt_mutex: Introduce rt_mutex_init_waiter() · 50809358
      由 Peter Zijlstra 提交于 
      Since there's already two copies of this code, introduce a helper now
before adding a third one.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.950039479@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      50809358
    • P
      futex: Pull rt_mutex_futex_unlock() out from under hb->lock · 16ffa12d
      由 Peter Zijlstra 提交于 
      There's a number of 'interesting' problems, all caused by holding
hb->lock while doing the rt_mutex_unlock() equivalient.

Notably:

 - a PI inversion on hb->lock; and,

 - a SCHED_DEADLINE crash because of pointer instability.

The previous changes:

 - changed the locking rules to cover {uval,pi_state} with wait_lock.

 - allow to do rt_mutex_futex_unlock() without dropping wait_lock; which in
   turn allows to rely on wait_lock atomicity completely.

 - simplified the waiter conundrum.

It's now sufficient to hold rtmutex::wait_lock and a reference on the
pi_state to protect the state consistency, so hb->lock can be dropped
before calling rt_mutex_futex_unlock().
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.900002056@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      16ffa12d
    • P
      futex: Rework inconsistent rt_mutex/futex_q state · 73d786bd
      由 Peter Zijlstra 提交于 
      There is a weird state in the futex_unlock_pi() path when it interleaves
with a concurrent futex_lock_pi() at the point where it drops hb->lock.

In this case, it can happen that the rt_mutex wait_list and the futex_q
disagree on pending waiters, in particular rt_mutex will find no pending
waiters where futex_q thinks there are. In this case the rt_mutex unlock
code cannot assign an owner.

The futex side fixup code has to cleanup the inconsistencies with quite a
bunch of interesting corner cases.

Simplify all this by changing wake_futex_pi() to return -EAGAIN when this
situation occurs. This then gives the futex_lock_pi() code the opportunity
to continue and the retried futex_unlock_pi() will now observe a coherent
state.

The only problem is that this breaks RT timeliness guarantees. That
is, consider the following scenario:

  T1 and T2 are both pinned to CPU0. prio(T2) > prio(T1)

    CPU0

    T1
      lock_pi()
      queue_me()  <- Waiter is visible

    preemption

    T2
      unlock_pi()
	loops with -EAGAIN forever

Which is undesirable for PI primitives. Future patches will rectify
this.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.850383690@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      73d786bd
    • P
      futex: Cleanup refcounting · bf92cf3a
      由 Peter Zijlstra 提交于 
      Add a put_pit_state() as counterpart for get_pi_state() so the refcounting
becomes consistent.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.801778516@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      bf92cf3a
    • P
      futex: Change locking rules · 734009e9
      由 Peter Zijlstra 提交于 
      Currently futex-pi relies on hb->lock to serialize everything. But hb->lock
creates another set of problems, especially priority inversions on RT where
hb->lock becomes a rt_mutex itself.

The rt_mutex::wait_lock is the most obvious protection for keeping the
futex user space value and the kernel internal pi_state in sync.

Rework and document the locking so rt_mutex::wait_lock is held accross all
operations which modify the user space value and the pi state.

This allows to invoke rt_mutex_unlock() (including deboost) without holding
hb->lock as a next step.

Nothing yet relies on the new locking rules.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.751993333@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      734009e9
    • P
      futex,rt_mutex: Provide futex specific rt_mutex API · 5293c2ef
      由 Peter Zijlstra 提交于 
      Part of what makes futex_unlock_pi() intricate is that
rt_mutex_futex_unlock() -> rt_mutex_slowunlock() can drop
rt_mutex::wait_lock.

This means it cannot rely on the atomicy of wait_lock, which would be
preferred in order to not rely on hb->lock so much.

The reason rt_mutex_slowunlock() needs to drop wait_lock is because it can
race with the rt_mutex fastpath, however futexes have their own fast path.

Since futexes already have a bunch of separate rt_mutex accessors, complete
that set and implement a rt_mutex variant without fastpath for them.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.702962446@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      5293c2ef
    • P
      futex: Use smp_store_release() in mark_wake_futex() · 1b367ece
      由 Peter Zijlstra 提交于 
      Since the futex_q can dissapear the instruction after assigning NULL,
this really should be a RELEASE barrier. That stops loads from hitting
dead memory too.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.604296452@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      1b367ece
    • P
      futex: Cleanup variable names for futex_top_waiter() · 499f5aca
      由 Peter Zijlstra 提交于 
      futex_top_waiter() returns the top-waiter on the pi_mutex. Assinging
this to a variable 'match' totally obscures the code.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.554710645@infradead.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      499f5aca
  49. 15 3月, 2017 1 次提交