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  1. 27 11月, 2012 1 次提交
    • D
      futex: avoid wake_futex() for a PI futex_q · aa10990e
      由 Darren Hart 提交于 
      Dave Jones reported a bug with futex_lock_pi() that his trinity test
exposed.  Sometime between queue_me() and taking the q.lock_ptr, the
lock_ptr became NULL, resulting in a crash.

While futex_wake() is careful to not call wake_futex() on futex_q's with
a pi_state or an rt_waiter (which are either waiting for a
futex_unlock_pi() or a PI futex_requeue()), futex_wake_op() and
futex_requeue() do not perform the same test.

Update futex_wake_op() and futex_requeue() to test for q.pi_state and
q.rt_waiter and abort with -EINVAL if detected.  To ensure any future
breakage is caught, add a WARN() to wake_futex() if the same condition
is true.

This fix has seen 3 hours of testing with "trinity -c futex" on an
x86_64 VM with 4 CPUS.

[akpm@linux-foundation.org: tidy up the WARN()]
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Reported-by: NDave Jones <davej@redat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: John Kacur <jkacur@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      aa10990e
  3. 01 11月, 2012 1 次提交
    • T
      futex: Handle futex_pi OWNER_DIED take over correctly · 59fa6245
      由 Thomas Gleixner 提交于 
      Siddhesh analyzed a failure in the take over of pi futexes in case the
owner died and provided a workaround.
See: http://sourceware.org/bugzilla/show_bug.cgi?id=14076

The detailed problem analysis shows:

Futex F is initialized with PTHREAD_PRIO_INHERIT and
PTHREAD_MUTEX_ROBUST_NP attributes.

T1 lock_futex_pi(F);

T2 lock_futex_pi(F);
   --> T2 blocks on the futex and creates pi_state which is associated
       to T1.

T1 exits
   --> exit_robust_list() runs
       --> Futex F userspace value TID field is set to 0 and
           FUTEX_OWNER_DIED bit is set.

T3 lock_futex_pi(F);
   --> Succeeds due to the check for F's userspace TID field == 0
   --> Claims ownership of the futex and sets its own TID into the
       userspace TID field of futex F
   --> returns to user space

T1 --> exit_pi_state_list()
       --> Transfers pi_state to waiter T2 and wakes T2 via
       	   rt_mutex_unlock(&pi_state->mutex)

T2 --> acquires pi_state->mutex and gains real ownership of the
       pi_state
   --> Claims ownership of the futex and sets its own TID into the
       userspace TID field of futex F
   --> returns to user space

T3 --> observes inconsistent state

This problem is independent of UP/SMP, preemptible/non preemptible
kernels, or process shared vs. private. The only difference is that
certain configurations are more likely to expose it.

So as Siddhesh correctly analyzed the following check in
futex_lock_pi_atomic() is the culprit:

	if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {

We check the userspace value for a TID value of 0 and take over the
futex unconditionally if that's true.

AFAICT this check is there as it is correct for a different corner
case of futexes: the WAITERS bit became stale.

Now the proposed change

-	if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
+       if (unlikely(ownerdied ||
+                       !(curval & (FUTEX_TID_MASK | FUTEX_WAITERS)))) {

solves the problem, but it's not obvious why and it wreckages the
"stale WAITERS bit" case.

What happens is, that due to the WAITERS bit being set (T2 is blocked
on that futex) it enforces T3 to go through lookup_pi_state(), which
in the above case returns an existing pi_state and therefor forces T3
to legitimately fight with T2 over the ownership of the pi_state (via
pi_state->mutex). Probelm solved!

Though that does not work for the "WAITERS bit is stale" problem
because if lookup_pi_state() does not find existing pi_state it
returns -ERSCH (due to TID == 0) which causes futex_lock_pi() to
return -ESRCH to user space because the OWNER_DIED bit is not set.

Now there is a different solution to that problem. Do not look at the
user space value at all and enforce a lookup of possibly available
pi_state. If pi_state can be found, then the new incoming locker T3
blocks on that pi_state and legitimately races with T2 to acquire the
rt_mutex and the pi_state and therefor the proper ownership of the
user space futex.

lookup_pi_state() has the correct order of checks. It first tries to
find a pi_state associated with the user space futex and only if that
fails it checks for futex TID value = 0. If no pi_state is available
nothing can create new state at that point because this happens with
the hash bucket lock held.

So the above scenario changes to:

T1 lock_futex_pi(F);

T2 lock_futex_pi(F);
   --> T2 blocks on the futex and creates pi_state which is associated
       to T1.

T1 exits
   --> exit_robust_list() runs
       --> Futex F userspace value TID field is set to 0 and
           FUTEX_OWNER_DIED bit is set.

T3 lock_futex_pi(F);
   --> Finds pi_state and blocks on pi_state->rt_mutex

T1 --> exit_pi_state_list()
       --> Transfers pi_state to waiter T2 and wakes it via
       	   rt_mutex_unlock(&pi_state->mutex)

T2 --> acquires pi_state->mutex and gains ownership of the pi_state
   --> Claims ownership of the futex and sets its own TID into the
       userspace TID field of futex F
   --> returns to user space

This covers all gazillion points on which T3 might come in between
T1's exit_robust_list() clearing the TID field and T2 fixing it up. It
also solves the "WAITERS bit stale" problem by forcing the take over.

Another benefit of changing the code this way is that it makes it less
dependent on untrusted user space values and therefor minimizes the
possible wreckage which might be inflicted.

As usual after staring for too long at the futex code my brain hurts
so much that I really want to ditch that whole optimization of
avoiding the syscall for the non contended case for PI futexes and rip
out the maze of corner case handling code. Unfortunately we can't as
user space relies on that existing behaviour, but at least thinking
about it helps me to preserve my mental sanity. Maybe we should
nevertheless :)
Reported-and-tested-by: NSiddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1210232138540.2756@ionosAcked-by: NDarren Hart <dvhart@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      59fa6245
  5. 24 7月, 2012 3 次提交
  7. 29 3月, 2012 2 次提交
  9. 15 2月, 2012 2 次提交
  11. 01 1月, 2012 1 次提交
    • H
      futex: Fix uninterruptible loop due to gate_area · e6780f72
      由 Hugh Dickins 提交于 
      It was found (by Sasha) that if you use a futex located in the gate
area we get stuck in an uninterruptible infinite loop, much like the
ZERO_PAGE issue.

While looking at this problem, PeterZ realized you'll get into similar
trouble when hitting any install_special_pages() mapping.  And are there
still drivers setting up their own special mmaps without page->mapping,
and without special VM or pte flags to make get_user_pages fail?

In most cases, if page->mapping is NULL, we do not need to retry at all:
Linus points out that even /proc/sys/vm/drop_caches poses no problem,
because it ends up using remove_mapping(), which takes care not to
interfere when the page reference count is raised.

But there is still one case which does need a retry: if memory pressure
called shmem_writepage in between get_user_pages_fast dropping page
table lock and our acquiring page lock, then the page gets switched from
filecache to swapcache (and ->mapping set to NULL) whatever the refcount.
Fault it back in to get the page->mapping needed for key->shared.inode.
Reported-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NHugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e6780f72
  13. 31 10月, 2011 1 次提交
  15. 15 9月, 2011 2 次提交
  17. 27 7月, 2011 1 次提交
    • S
      futex: Fix regression with read only mappings · 9ea71503
      由 Shawn Bohrer 提交于 
      commit 7485d0d3 (futexes: Remove rw
parameter from get_futex_key()) in 2.6.33 fixed two problems:  First, It
prevented a loop when encountering a ZERO_PAGE. Second, it fixed RW
MAP_PRIVATE futex operations by forcing the COW to occur by
unconditionally performing a write access get_user_pages_fast() to get
the page.  The commit also introduced a user-mode regression in that it
broke futex operations on read-only memory maps.  For example, this
breaks workloads that have one or more reader processes doing a
FUTEX_WAIT on a futex within a read only shared file mapping, and a
writer processes that has a writable mapping issuing the FUTEX_WAKE.

This fixes the regression for valid futex operations on RO mappings by
trying a RO get_user_pages_fast() when the RW get_user_pages_fast()
fails. This change makes it necessary to also check for invalid use
cases, such as anonymous RO mappings (which can never change) and the
ZERO_PAGE which the commit referenced above was written to address.

This patch does restore the original behavior with RO MAP_PRIVATE
mappings, which have inherent user-mode usage problems and don't really
make sense.  With this patch performing a FUTEX_WAIT within a RO
MAP_PRIVATE mapping will be successfully woken provided another process
updates the region of the underlying mapped file.  However, the mmap()
man page states that for a MAP_PRIVATE mapping:

  It is unspecified whether changes made to the file after
  the mmap() call are visible in the mapped region.

So user-mode users attempting to use futex operations on RO MAP_PRIVATE
mappings are depending on unspecified behavior.  Additionally a
RO MAP_PRIVATE mapping could fail to wake up in the following case.

  Thread-A: call futex(FUTEX_WAIT, memory-region-A).
            get_futex_key() return inode based key.
            sleep on the key
  Thread-B: call mprotect(PROT_READ|PROT_WRITE, memory-region-A)
  Thread-B: write memory-region-A.
            COW happen. This process's memory-region-A become related
            to new COWed private (ie PageAnon=1) page.
  Thread-B: call futex(FUETX_WAKE, memory-region-A).
            get_futex_key() return mm based key.
            IOW, we fail to wake up Thread-A.

Once again doing something like this is just silly and users who do
something like this get what they deserve.

While RO MAP_PRIVATE mappings are nonsensical, checking for a private
mapping requires walking the vmas and was deemed too costly to avoid a
userspace hang.

This Patch is based on Peter Zijlstra's initial patch with modifications to
only allow RO mappings for futex operations that need VERIFY_READ access.
Reported-by: NDavid Oliver <david@rgmadvisors.com>
Signed-off-by: NShawn Bohrer <sbohrer@rgmadvisors.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: peterz@infradead.org
Cc: eric.dumazet@gmail.com
Cc: zvonler@rgmadvisors.com
Cc: hughd@google.com
Link: http://lkml.kernel.org/r/1309450892-30676-1-git-send-email-sbohrer@rgmadvisors.com
Cc: stable@kernel.org
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      9ea71503
  19. 26 7月, 2011 1 次提交
    • B
      mm/futex: fix futex writes on archs with SW tracking of dirty & young · 2efaca92
      由 Benjamin Herrenschmidt 提交于 
      I haven't reproduced it myself but the fail scenario is that on such
machines (notably ARM and some embedded powerpc), if you manage to hit
that futex path on a writable page whose dirty bit has gone from the PTE,
you'll livelock inside the kernel from what I can tell.

It will go in a loop of trying the atomic access, failing, trying gup to
"fix it up", getting succcess from gup, go back to the atomic access,
failing again because dirty wasn't fixed etc...

So I think you essentially hang in the kernel.

The scenario is probably rare'ish because affected architecture are
embedded and tend to not swap much (if at all) so we probably rarely hit
the case where dirty is missing or young is missing, but I think Shan has
a piece of SW that can reliably reproduce it using a shared writable
mapping & fork or something like that.

On archs who use SW tracking of dirty & young, a page without dirty is
effectively mapped read-only and a page without young unaccessible in the
PTE.

Additionally, some architectures might lazily flush the TLB when relaxing
write protection (by doing only a local flush), and expect a fault to
invalidate the stale entry if it's still present on another processor.

The futex code assumes that if the "in_atomic()" access -EFAULT's, it can
"fix it up" by causing get_user_pages() which would then be equivalent to
taking the fault.

However that isn't the case.  get_user_pages() will not call
handle_mm_fault() in the case where the PTE seems to have the right
permissions, regardless of the dirty and young state.  It will eventually
update those bits ...  in the struct page, but not in the PTE.

Additionally, it will not handle the lazy TLB flushing that can be
required by some architectures in the fault case.

Basically, gup is the wrong interface for the job.  The patch provides a
more appropriate one which boils down to just calling handle_mm_fault()
since what we are trying to do is simulate a real page fault.

The futex code currently attempts to write to user memory within a
pagefault disabled section, and if that fails, tries to fix it up using
get_user_pages().

This doesn't work on archs where the dirty and young bits are maintained
by software, since they will gate access permission in the TLB, and will
not be updated by gup().

In addition, there's an expectation on some archs that a spurious write
fault triggers a local TLB flush, and that is missing from the picture as
well.

I decided that adding those "features" to gup() would be too much for this
already too complex function, and instead added a new simpler
fixup_user_fault() which is essentially a wrapper around handle_mm_fault()
which the futex code can call.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix some nits Darren saw, fiddle comment layout]
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Reported-by: NShan Hai <haishan.bai@gmail.com>
Tested-by: NShan Hai <haishan.bai@gmail.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Darren Hart <darren.hart@intel.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      2efaca92
  21. 08 7月, 2011 1 次提交
  23. 15 4月, 2011 1 次提交
  25. 25 3月, 2011 1 次提交
  27. 24 3月, 2011 1 次提交
  29. 15 3月, 2011 1 次提交
    • T
      futex: Deobfuscate handle_futex_death() · 6e0aa9f8
      由 Thomas Gleixner 提交于 
      handle_futex_death() uses futex_atomic_cmpxchg_inatomic() without
disabling page faults. That's ok, but totally non obvious.

We don't hold locks so we actually can and want to fault here, because
the get_user() before futex_atomic_cmpxchg_inatomic() does not
guarantee a R/W mapping.

We could just add a big fat comment to explain this, but actually
changing the code so that the functionality is entirely clear is
better.

Use the helper function which disables page faults around the
futex_atomic_cmpxchg_inatomic() and handle a fault with a call to
fault_in_user_writeable() as all other places in the futex code do as
well.
Pointed-out-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NDarren Hart <darren@dvhart.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
LKML-Reference: <alpine.LFD.2.00.1103141126590.2787@localhost6.localdomain6>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      6e0aa9f8
  31. 12 3月, 2011 2 次提交
  33. 11 3月, 2011 3 次提交
    • M
      futex: Sanitize cmpxchg_futex_value_locked API · 37a9d912
      由 Michel Lespinasse 提交于 
      The cmpxchg_futex_value_locked API was funny in that it returned either
the original, user-exposed futex value OR an error code such as -EFAULT.
This was confusing at best, and could be a source of livelocks in places
that retry the cmpxchg_futex_value_locked after trying to fix the issue
by running fault_in_user_writeable().
    
This change makes the cmpxchg_futex_value_locked API more similar to the
get_futex_value_locked one, returning an error code and updating the
original value through a reference argument.
Signed-off-by: NMichel Lespinasse <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>  [tile]
Acked-by: Tony Luck <tony.luck@intel.com>  [ia64]
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Simek <monstr@monstr.eu>  [microblaze]
Acked-by: David Howells <dhowells@redhat.com> [frv]
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311024851.GC26122@google.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      37a9d912
    • T
      futex: Avoid redudant evaluation of task_pid_vnr() · c0c9ed15
      由 Thomas Gleixner 提交于 
      The result is not going to change under us, so no need to reevaluate
this over and over. Seems to be a leftover from the mechanical mass
conversion of task->pid to task_pid_vnr(tsk).
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      c0c9ed15
    • M
      futex: Update futex_wait_setup comments about locking · 8fe8f545
      由 Michel Lespinasse 提交于 
      Reviving a cleanup I had done about a year ago as part of a larger
futex_set_wait proposal. Over the years, the locking of the hashed
futex queue got improved, so that some of the "rare but normal" race
conditions described in comments can't actually happen anymore.
Signed-off-by: NMichel Lespinasse <walken@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Darren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20110307020750.GA31188@google.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      8fe8f545
  35. 28 1月, 2011 1 次提交
    • L
      rtmutex: Simplify PI algorithm and make highest prio task get lock · 8161239a
      由 Lai Jiangshan 提交于 
      In current rtmutex, the pending owner may be boosted by the tasks
in the rtmutex's waitlist when the pending owner is deboosted
or a task in the waitlist is boosted. This boosting is unrelated,
because the pending owner does not really take the rtmutex.
It is not reasonable.

Example.

time1:
A(high prio) onwers the rtmutex.
B(mid prio) and C (low prio) in the waitlist.

time2
A release the lock, B becomes the pending owner
A(or other high prio task) continues to run. B's prio is lower
than A, so B is just queued at the runqueue.

time3
A or other high prio task sleeps, but we have passed some time
The B and C's prio are changed in the period (time2 ~ time3)
due to boosting or deboosting. Now C has the priority higher
than B. ***Is it reasonable that C has to boost B and help B to
get the rtmutex?

NO!! I think, it is unrelated/unneed boosting before B really
owns the rtmutex. We should give C a chance to beat B and
win the rtmutex.

This is the motivation of this patch. This patch *ensures*
only the top waiter or higher priority task can take the lock.

How?
1) we don't dequeue the top waiter when unlock, if the top waiter
   is changed, the old top waiter will fail and go to sleep again.
2) when requiring lock, it will get the lock when the lock is not taken and:
   there is no waiter OR higher priority than waiters OR it is top waiter.
3) In any time, the top waiter is changed, the top waiter will be woken up.

The algorithm is much simpler than before, no pending owner, no
boosting for pending owner.

Other advantage of this patch:
1) The states of a rtmutex are reduced a half, easier to read the code.
2) the codes become shorter.
3) top waiter is not dequeued until it really take the lock:
   they will retain FIFO when it is stolen.

Not advantage nor disadvantage
1) Even we may wakeup multiple waiters(any time when top waiter changed),
   we hardly cause "thundering herd",
   the number of wokenup task is likely 1 or very little.
2) two APIs are changed.
   rt_mutex_owner() will not return pending owner, it will return NULL when
                    the top waiter is going to take the lock.
   rt_mutex_next_owner() always return the top waiter.
	                 will not return NULL if we have waiters
                         because the top waiter is not dequeued.

   I have fixed the code that use these APIs.

need updated after this patch is accepted
1) Document/*
2) the testcase scripts/rt-tester/t4-l2-pi-deboost.tst
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4D3012D5.4060709@cn.fujitsu.com>
Reviewed-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      8161239a
  37. 14 1月, 2011 1 次提交
    • A
      thp: update futex compound knowledge · a5b338f2
      由 Andrea Arcangeli 提交于 
      Futex code is smarter than most other gup_fast O_DIRECT code and knows
about the compound internals.  However now doing a put_page(head_page)
will not release the pin on the tail page taken by gup-fast, leading to
all sort of refcounting bugchecks.  Getting a stable head_page is a little
tricky.

page_head = page is there because if this is not a tail page it's also the
page_head.  Only in case this is a tail page, compound_head is called,
otherwise it's guaranteed unnecessary.  And if it's a tail page
compound_head has to run atomically inside irq disabled section
__get_user_pages_fast before returning.  Otherwise ->first_page won't be a
stable pointer.

Disableing irq before __get_user_page_fast and releasing irq after running
compound_head is needed because if __get_user_page_fast returns == 1, it
means the huge pmd is established and cannot go away from under us.
pmdp_splitting_flush_notify in __split_huge_page_splitting will have to
wait for local_irq_enable before the IPI delivery can return.  This means
__split_huge_page_refcount can't be running from under us, and in turn
when we run compound_head(page) we're not reading a dangling pointer from
tailpage->first_page.  Then after we get to stable head page, we are
always safe to call compound_lock and after taking the compound lock on
head page we can finally re-check if the page returned by gup-fast is
still a tail page.  in which case we're set and we didn't need to split
the hugepage in order to take a futex on it.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a5b338f2
  39. 11 1月, 2011 1 次提交
  41. 10 11月, 2010 4 次提交
    • D
      futex: Add futex_q static initializer · 5bdb05f9
      由 Darren Hart 提交于 
      The futex_q struct has grown considerably over the last couple years. I
believe it now merits a static initializer to avoid uninitialized data
errors (having spent more time than I care to admit debugging an uninitialized
q.bitset in an experimental new op code).

With the key initializer built in, several of the FUTEX_KEY_INIT calls can
be removed.

V2: use a static variable instead of an init macro.
    use a C99 initializer and don't rely on variable ordering in the struct.
V3: make futex_q_init const
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1289252428-18383-1-git-send-email-dvhart@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      5bdb05f9
    • D
      futex: Replace fshared and clockrt with combined flags · b41277dc
      由 Darren Hart 提交于 
      In the early days we passed the mmap sem around. That became the
"int fshared" with the fast gup improvements. Then we added
"int clockrt" in places. This patch unifies these options as "flags".

[ tglx: Split out the stale fshared cleanup ]
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1289250609-16304-1-git-send-email-dvhart@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      b41277dc
    • T
      futex: Cleanup stale fshared flag interfaces · ae791a2d
      由 Thomas Gleixner 提交于 
      The fast GUP changes stopped using the fshared flag in
put_futex_keys(), but we kept the interface the same.

Cleanup all stale users.

This patch is split out from Darren Harts combo patch which also
combines various flags. This way the changes are clearly separated.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Darren Hart <dvhart@linux.intel.com>
LKML-Reference: <1289250609-16304-1-git-send-email-dvhart@linux.intel.com>
      ae791a2d
    • D
      futex: Address compiler warnings in exit_robust_list · 4c115e95
      由 Darren Hart 提交于 
      Since commit 1dcc41bb (futex: Change 3rd arg of fetch_robust_entry()
to unsigned int*) some gcc versions decided to emit the following
warning:

kernel/futex.c: In function ‘exit_robust_list’:
kernel/futex.c:2492: warning: ‘next_pi’ may be used uninitialized in this function

The commit did not introduce the warning as gcc should have warned
before that commit as well. It's just gcc being silly.

The code path really can't result in next_pi being unitialized (or
should not), but let's keep the build clean. Annotate next_pi as an
uninitialized_var.

[ tglx: Addressed the same issue in futex_compat.c and massaged the
  	changelog ]
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Tested-by: NMatt Fleming <matt@console-pimps.org>
Tested-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1288897200-13008-1-git-send-email-dvhart@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      4c115e95
  43. 26 10月, 2010 1 次提交
  45. 19 10月, 2010 1 次提交
    • D
      futex: Fix errors in nested key ref-counting · 7ada876a
      由 Darren Hart 提交于 
      futex_wait() is leaking key references due to futex_wait_setup()
acquiring an additional reference via the queue_lock() routine. The
nested key ref-counting has been masking bugs and complicating code
analysis. queue_lock() is only called with a previously ref-counted
key, so remove the additional ref-counting from the queue_(un)lock()
functions.

Also futex_wait_requeue_pi() drops one key reference too many in
unqueue_me_pi(). Remove the key reference handling from
unqueue_me_pi(). This was paired with a queue_lock() in
futex_lock_pi(), so the count remains unchanged.

Document remaining nested key ref-counting sites.
Signed-off-by: NDarren Hart <dvhart@linux.intel.com>
Reported-and-tested-by: Matthieu Fertré<matthieu.fertre@kerlabs.com>
Reported-by: Louis Rilling<louis.rilling@kerlabs.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <4CBB17A8.70401@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
      7ada876a
  47. 14 10月, 2010 1 次提交
  49. 18 9月, 2010 3 次提交
  51. 01 7月, 2010 1 次提交
    • M
      futex: futex_find_get_task remove credentails check · 7a0ea09a
      由 Michal Hocko 提交于 
      futex_find_get_task is currently used (through lookup_pi_state) from two
contexts, futex_requeue and futex_lock_pi_atomic.  None of the paths
looks it needs the credentials check, though.  Different (e)uids
shouldn't matter at all because the only thing that is important for
shared futex is the accessibility of the shared memory.

The credentail check results in glibc assert failure or process hang (if
glibc is compiled without assert support) for shared robust pthread
mutex with priority inheritance if a process tries to lock already held
lock owned by a process with a different euid:

pthread_mutex_lock.c:312: __pthread_mutex_lock_full: Assertion `(-(e)) != 3 || !robust' failed.

The problem is that futex_lock_pi_atomic which is called when we try to
lock already held lock checks the current holder (tid is stored in the
futex value) to get the PI state.  It uses lookup_pi_state which in turn
gets task struct from futex_find_get_task.  ESRCH is returned either
when the task is not found or if credentials check fails.

futex_lock_pi_atomic simply returns if it gets ESRCH.  glibc code,
however, doesn't expect that robust lock returns with ESRCH because it
should get either success or owner died.
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NDarren Hart <dvhltc@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      7a0ea09a
  53. 03 2月, 2010 1 次提交