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  1. 12 10月, 2016 3 次提交
    • D
      ipc/msg: batch queue sender wakeups · e3658538
      由 Davidlohr Bueso 提交于 
      Currently the use of wake_qs in sysv msg queues are only for the receiver
tasks that are blocked on the queue.  But blocked sender tasks (due to
queue size constraints) still are awoken with the ipc object lock held,
which can be a problem particularly for small sized queues and far from
gracious for -rt (just like it was for the receiver side).

The paths that actually wakeup a sender are obviously related to when we
are either getting rid of the queue or after (some) space is freed-up
after a receiver takes the msg (msgrcv).  Furthermore, with the exception
of msgrcv, we can always piggy-back on expunge_all that has its own tasks
lined-up for waking.  Finally, upon unlinking the message, it should be no
problem delaying the wakeups a bit until after we've released the lock.

Link: http://lkml.kernel.org/r/1469748819-19484-3-git-send-email-dave@stgolabs.netSigned-off-by: NDavidlohr Bueso <dbueso@suse.de>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e3658538
    • S
      ipc/msg: implement lockless pipelined wakeups · ee51636c
      由 Sebastian Andrzej Siewior 提交于 
      This patch moves the wakeup_process() invocation so it is not done under
the ipc global lock by making use of a lockless wake_q.  With this change,
the waiter is woken up once the message has been assigned and it does not
need to loop on SMP if the message points to NULL.  In the signal case we
still need to check the pointer under the lock to verify the state.

This change should also avoid the introduction of preempt_disable() in -RT
which avoids a busy-loop which pools for the NULL -> !NULL change if the
waiter has a higher priority compared to the waker.

By making use of wake_qs, the logic of sysv msg queues is greatly
simplified (and very well suited as we can batch lockless wakeups),
particularly around the lockless receive algorithm.

This has been tested with Manred's pmsg-shared tool on a "AMD A10-7800
Radeon R7, 12 Compute Cores 4C+8G":

test             |   before   |   after    | diff
-----------------|------------|------------|----------
pmsg-shared 8 60 | 19,347,422 | 30,442,191 | + ~57.34 %
pmsg-shared 4 60 | 21,367,197 | 35,743,458 | + ~67.28 %
pmsg-shared 2 60 | 22,884,224 | 24,278,200 | +  ~6.09 %

Link: http://lkml.kernel.org/r/1469748819-19484-2-git-send-email-dave@stgolabs.netSigned-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ee51636c
    • M
      ipc/sem.c: fix complex_count vs. simple op race · 5864a2fd
      由 Manfred Spraul 提交于 
      Commit 6d07b68c ("ipc/sem.c: optimize sem_lock()") introduced a
race:

sem_lock has a fast path that allows parallel simple operations.
There are two reasons why a simple operation cannot run in parallel:
 - a non-simple operations is ongoing (sma->sem_perm.lock held)
 - a complex operation is sleeping (sma->complex_count != 0)

As both facts are stored independently, a thread can bypass the current
checks by sleeping in the right positions.  See below for more details
(or kernel bugzilla 105651).

The patch fixes that by creating one variable (complex_mode)
that tracks both reasons why parallel operations are not possible.

The patch also updates stale documentation regarding the locking.

With regards to stable kernels:
The patch is required for all kernels that include the
commit 6d07b68c ("ipc/sem.c: optimize sem_lock()") (3.10?)

The alternative is to revert the patch that introduced the race.

The patch is safe for backporting, i.e. it makes no assumptions
about memory barriers in spin_unlock_wait().

Background:
Here is the race of the current implementation:

Thread A: (simple op)
- does the first "sma->complex_count == 0" test

Thread B: (complex op)
- does sem_lock(): This includes an array scan. But the scan can't
  find Thread A, because Thread A does not own sem->lock yet.
- the thread does the operation, increases complex_count,
  drops sem_lock, sleeps

Thread A:
- spin_lock(&sem->lock), spin_is_locked(sma->sem_perm.lock)
- sleeps before the complex_count test

Thread C: (complex op)
- does sem_lock (no array scan, complex_count==1)
- wakes up Thread B.
- decrements complex_count

Thread A:
- does the complex_count test

Bug:
Now both thread A and thread C operate on the same array, without
any synchronization.

Fixes: 6d07b68c ("ipc/sem.c: optimize sem_lock()")
Link: http://lkml.kernel.org/r/1469123695-5661-1-git-send-email-manfred@colorfullife.com
Reported-by: <felixh@informatik.uni-bremen.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: <1vier1@web.de>
Cc: <stable@vger.kernel.org>	[3.10+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5864a2fd
  3. 28 9月, 2016 1 次提交
  5. 23 9月, 2016 2 次提交
  7. 09 8月, 2016 1 次提交
  9. 03 8月, 2016 2 次提交
  11. 27 7月, 2016 2 次提交
  13. 24 6月, 2016 4 次提交
  15. 14 6月, 2016 2 次提交
  17. 24 5月, 2016 1 次提交
  19. 05 4月, 2016 1 次提交
    • K
      mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros · 09cbfeaf
      由 Kirill A. Shutemov 提交于 
      PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.

This promise never materialized.  And unlikely will.

We have many places where PAGE_CACHE_SIZE assumed to be equal to
PAGE_SIZE.  And it's constant source of confusion on whether
PAGE_CACHE_* or PAGE_* constant should be used in a particular case,
especially on the border between fs and mm.

Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
breakage to be doable.

Let's stop pretending that pages in page cache are special.  They are
not.

The changes are pretty straight-forward:

 - <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - <foo> >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};

 - page_cache_get() -> get_page();

 - page_cache_release() -> put_page();

This patch contains automated changes generated with coccinelle using
script below.  For some reason, coccinelle doesn't patch header files.
I've called spatch for them manually.

The only adjustment after coccinelle is revert of changes to
PAGE_CAHCE_ALIGN definition: we are going to drop it later.

There are few places in the code where coccinelle didn't reach.  I'll
fix them manually in a separate patch.  Comments and documentation also
will be addressed with the separate patch.

virtual patch

@@
expression E;
@@
- E << (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
expression E;
@@
- E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
@@
- PAGE_CACHE_SHIFT
+ PAGE_SHIFT

@@
@@
- PAGE_CACHE_SIZE
+ PAGE_SIZE

@@
@@
- PAGE_CACHE_MASK
+ PAGE_MASK

@@
expression E;
@@
- PAGE_CACHE_ALIGN(E)
+ PAGE_ALIGN(E)

@@
expression E;
@@
- page_cache_get(E)
+ get_page(E)

@@
expression E;
@@
- page_cache_release(E)
+ put_page(E)
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      09cbfeaf
  21. 23 3月, 2016 1 次提交
    • D
      ipc/sem: make semctl setting sempid consistent · a5f4db87
      由 Davidlohr Bueso 提交于 
      As indicated by bug#112271, Linux sets the sempid value upon semctl, and
not only for semop calls.  However, within semctl we only do this for
SETVAL, leaving SETALL without updating the field, and therefore rather
inconsistent behavior when compared to other Unices.

There is really no documentation regarding this and therefore users
should not make assumptions.  With this patch, along with updating
semctl.2 manpages, this scenario should become less ambiguous As such,
set sempid on SETALL cmd.

Also update some in-code documentation, specifying where the sempid is
set.

Passes ltp and custom testcase where a child (fork) does SETALL to the
set.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Reported-by: NPhilip Semanchuk <linux_kernel.20.ick@spamgourmet.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Herton R. Krzesinski <herton@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a5f4db87
  23. 19 2月, 2016 1 次提交
  25. 23 1月, 2016 2 次提交
  27. 21 1月, 2016 1 次提交
  29. 15 1月, 2016 1 次提交
    • V
      kmemcg: account certain kmem allocations to memcg · 5d097056
      由 Vladimir Davydov 提交于 
      Mark those kmem allocations that are known to be easily triggered from
userspace as __GFP_ACCOUNT/SLAB_ACCOUNT, which makes them accounted to
memcg.  For the list, see below:

 - threadinfo
 - task_struct
 - task_delay_info
 - pid
 - cred
 - mm_struct
 - vm_area_struct and vm_region (nommu)
 - anon_vma and anon_vma_chain
 - signal_struct
 - sighand_struct
 - fs_struct
 - files_struct
 - fdtable and fdtable->full_fds_bits
 - dentry and external_name
 - inode for all filesystems. This is the most tedious part, because
   most filesystems overwrite the alloc_inode method.

The list is far from complete, so feel free to add more objects.
Nevertheless, it should be close to "account everything" approach and
keep most workloads within bounds.  Malevolent users will be able to
breach the limit, but this was possible even with the former "account
everything" approach (simply because it did not account everything in
fact).

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: NVladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5d097056
  31. 07 11月, 2015 1 次提交
    • D
      ipc,msg: drop dst nil validation in copy_msg · 5f2a2d5d
      由 Davidlohr Bueso 提交于 
      d0edd852 ("ipc: convert invalid scenarios to use WARN_ON") relaxed the
nil dst parameter check, originally being a full BUG_ON.  However, this
check seems quite unnecessary when the only purpose is for
ceckpoint/restore (MSG_COPY flag):

o The copy variable is set initially to nil, apparently as a way of
  ensuring that prepare_copy is previously called.  Which is in fact done,
  unconditionally at the beginning of do_msgrcv.

o There is no concurrency with 'copy' (stack allocated in do_msgrcv).

Furthermore, any errors in 'copy' (and thus prepare_copy/copy_msg) should
always handled by IS_ERR() family.  Therefore remove this check altogether
as it can never occur with the current users.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5f2a2d5d
  33. 01 10月, 2015 1 次提交
    • L
      Initialize msg/shm IPC objects before doing ipc_addid() · b9a53227
      由 Linus Torvalds 提交于 
      As reported by Dmitry Vyukov, we really shouldn't do ipc_addid() before
having initialized the IPC object state.  Yes, we initialize the IPC
object in a locked state, but with all the lockless RCU lookup work,
that IPC object lock no longer means that the state cannot be seen.

We already did this for the IPC semaphore code (see commit e8577d1f:
"ipc/sem.c: fully initialize sem_array before making it visible") but we
clearly forgot about msg and shm.
Reported-by: NDmitry Vyukov <dvyukov@google.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      b9a53227
  35. 11 9月, 2015 1 次提交
    • D
      ipc: convert invalid scenarios to use WARN_ON · d0edd852
      由 Davidlohr Bueso 提交于 
      Considering Linus' past rants about the (ab)use of BUG in the kernel, I
took a look at how we deal with such calls in ipc.  Given that any errors
or corruption in ipc code are most likely contained within the set of
processes participating in the broken mechanisms, there aren't really many
strong fatal system failure scenarios that would require a BUG call.
Also, if something is seriously wrong, ipc might not be the place for such
a BUG either.

1. For example, recently, a customer hit one of these BUG_ONs in shm
   after failing shm_lock().  A busted ID imho does not merit a BUG_ON,
   and WARN would have been better.

2. MSG_COPY functionality of posix msgrcv(2) for checkpoint/restore.
   I don't see how we can hit this anyway -- at least it should be IS_ERR.
    The 'copy' arg from do_msgrcv is always set by calling prepare_copy()
   first and foremost.  We could also probably drop this check altogether.
    Either way, it does not merit a BUG_ON.

3. No ->fault() callback for the fs getting the corresponding page --
   seems selfish to make the system unusable.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      d0edd852
  37. 15 8月, 2015 3 次提交
    • M
      ipc/sem.c: update/correct memory barriers · 3ed1f8a9
      由 Manfred Spraul 提交于 
      sem_lock() did not properly pair memory barriers:

!spin_is_locked() and spin_unlock_wait() are both only control barriers.
The code needs an acquire barrier, otherwise the cpu might perform read
operations before the lock test.

As no primitive exists inside <include/spinlock.h> and since it seems
noone wants another primitive, the code creates a local primitive within
ipc/sem.c.

With regards to -stable:

The change of sem_wait_array() is a bugfix, the change to sem_lock() is a
nop (just a preprocessor redefinition to improve the readability).  The
bugfix is necessary for all kernels that use sem_wait_array() (i.e.:
starting from 3.10).
Signed-off-by: NManfred Spraul <manfred@colorfullife.com>
Reported-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: <stable@vger.kernel.org>	[3.10+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3ed1f8a9
    • H
      ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem() · a9795584
      由 Herton R. Krzesinski 提交于 
      After we acquire the sma->sem_perm lock in exit_sem(), we are protected
against a racing IPC_RMID operation.  Also at that point, we are the last
user of sem_undo_list.  Therefore it isn't required that we acquire or use
ulp->lock.
Signed-off-by: NHerton R. Krzesinski <herton@redhat.com>
Acked-by: NManfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Rafael Aquini <aquini@redhat.com>
CC: Aristeu Rozanski <aris@redhat.com>
Cc: David Jeffery <djeffery@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a9795584
    • H
      ipc,sem: fix use after free on IPC_RMID after a task using same semaphore set exits · 602b8593
      由 Herton R. Krzesinski 提交于 
      The current semaphore code allows a potential use after free: in
exit_sem we may free the task's sem_undo_list while there is still
another task looping through the same semaphore set and cleaning the
sem_undo list at freeary function (the task called IPC_RMID for the same
semaphore set).

For example, with a test program [1] running which keeps forking a lot
of processes (which then do a semop call with SEM_UNDO flag), and with
the parent right after removing the semaphore set with IPC_RMID, and a
kernel built with CONFIG_SLAB, CONFIG_SLAB_DEBUG and
CONFIG_DEBUG_SPINLOCK, you can easily see something like the following
in the kernel log:

   Slab corruption (Not tainted): kmalloc-64 start=ffff88003b45c1c0, len=64
   000: 6b 6b 6b 6b 6b 6b 6b 6b 00 6b 6b 6b 6b 6b 6b 6b  kkkkkkkk.kkkkkkk
   010: ff ff ff ff 6b 6b 6b 6b ff ff ff ff ff ff ff ff  ....kkkk........
   Prev obj: start=ffff88003b45c180, len=64
   000: 00 00 00 00 ad 4e ad de ff ff ff ff 5a 5a 5a 5a  .....N......ZZZZ
   010: ff ff ff ff ff ff ff ff c0 fb 01 37 00 88 ff ff  ...........7....
   Next obj: start=ffff88003b45c200, len=64
   000: 00 00 00 00 ad 4e ad de ff ff ff ff 5a 5a 5a 5a  .....N......ZZZZ
   010: ff ff ff ff ff ff ff ff 68 29 a7 3c 00 88 ff ff  ........h).<....
   BUG: spinlock wrong CPU on CPU#2, test/18028
   general protection fault: 0000 [#1] SMP
   Modules linked in: 8021q mrp garp stp llc nf_conntrack_ipv4 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables binfmt_misc ppdev input_leds joydev parport_pc parport floppy serio_raw virtio_balloon virtio_rng virtio_console virtio_net iosf_mbi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcspkr qxl ttm drm_kms_helper drm snd_hda_codec_generic i2c_piix4 snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore crc32c_intel virtio_pci virtio_ring virtio pata_acpi ata_generic [last unloaded: speedstep_lib]
   CPU: 2 PID: 18028 Comm: test Not tainted 4.2.0-rc5+ #1
   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014
   RIP: spin_dump+0x53/0xc0
   Call Trace:
     spin_bug+0x30/0x40
     do_raw_spin_unlock+0x71/0xa0
     _raw_spin_unlock+0xe/0x10
     freeary+0x82/0x2a0
     ? _raw_spin_lock+0xe/0x10
     semctl_down.clone.0+0xce/0x160
     ? __do_page_fault+0x19a/0x430
     ? __audit_syscall_entry+0xa8/0x100
     SyS_semctl+0x236/0x2c0
     ? syscall_trace_leave+0xde/0x130
     entry_SYSCALL_64_fastpath+0x12/0x71
   Code: 8b 80 88 03 00 00 48 8d 88 60 05 00 00 48 c7 c7 a0 2c a4 81 31 c0 65 8b 15 eb 40 f3 7e e8 08 31 68 00 4d 85 e4 44 8b 4b 08 74 5e <45> 8b 84 24 88 03 00 00 49 8d 8c 24 60 05 00 00 8b 53 04 48 89
   RIP  [<ffffffff810d6053>] spin_dump+0x53/0xc0
    RSP <ffff88003750fd68>
   ---[ end trace 783ebb76612867a0 ]---
   NMI watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [test:18053]
   Modules linked in: 8021q mrp garp stp llc nf_conntrack_ipv4 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables binfmt_misc ppdev input_leds joydev parport_pc parport floppy serio_raw virtio_balloon virtio_rng virtio_console virtio_net iosf_mbi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcspkr qxl ttm drm_kms_helper drm snd_hda_codec_generic i2c_piix4 snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore crc32c_intel virtio_pci virtio_ring virtio pata_acpi ata_generic [last unloaded: speedstep_lib]
   CPU: 3 PID: 18053 Comm: test Tainted: G      D         4.2.0-rc5+ #1
   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014
   RIP: native_read_tsc+0x0/0x20
   Call Trace:
     ? delay_tsc+0x40/0x70
     __delay+0xf/0x20
     do_raw_spin_lock+0x96/0x140
     _raw_spin_lock+0xe/0x10
     sem_lock_and_putref+0x11/0x70
     SYSC_semtimedop+0x7bf/0x960
     ? handle_mm_fault+0xbf6/0x1880
     ? dequeue_task_fair+0x79/0x4a0
     ? __do_page_fault+0x19a/0x430
     ? kfree_debugcheck+0x16/0x40
     ? __do_page_fault+0x19a/0x430
     ? __audit_syscall_entry+0xa8/0x100
     ? do_audit_syscall_entry+0x66/0x70
     ? syscall_trace_enter_phase1+0x139/0x160
     SyS_semtimedop+0xe/0x10
     SyS_semop+0x10/0x20
     entry_SYSCALL_64_fastpath+0x12/0x71
   Code: 47 10 83 e8 01 85 c0 89 47 10 75 08 65 48 89 3d 1f 74 ff 7e c9 c3 0f 1f 44 00 00 55 48 89 e5 e8 87 17 04 00 66 90 c9 c3 0f 1f 00 <55> 48 89 e5 0f 31 89 c1 48 89 d0 48 c1 e0 20 89 c9 48 09 c8 c9
   Kernel panic - not syncing: softlockup: hung tasks

I wasn't able to trigger any badness on a recent kernel without the
proper config debugs enabled, however I have softlockup reports on some
kernel versions, in the semaphore code, which are similar as above (the
scenario is seen on some servers running IBM DB2 which uses semaphore
syscalls).

The patch here fixes the race against freeary, by acquiring or waiting
on the sem_undo_list lock as necessary (exit_sem can race with freeary,
while freeary sets un->semid to -1 and removes the same sem_undo from
list_proc or when it removes the last sem_undo).

After the patch I'm unable to reproduce the problem using the test case
[1].

[1] Test case used below:

    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/sem.h>
    #include <sys/wait.h>
    #include <stdlib.h>
    #include <time.h>
    #include <unistd.h>
    #include <errno.h>

    #define NSEM 1
    #define NSET 5

    int sid[NSET];

    void thread()
    {
            struct sembuf op;
            int s;
            uid_t pid = getuid();

            s = rand() % NSET;
            op.sem_num = pid % NSEM;
            op.sem_op = 1;
            op.sem_flg = SEM_UNDO;

            semop(sid[s], &op, 1);
            exit(EXIT_SUCCESS);
    }

    void create_set()
    {
            int i, j;
            pid_t p;
            union {
                    int val;
                    struct semid_ds *buf;
                    unsigned short int *array;
                    struct seminfo *__buf;
            } un;

            /* Create and initialize semaphore set */
            for (i = 0; i < NSET; i++) {
                    sid[i] = semget(IPC_PRIVATE , NSEM, 0644 | IPC_CREAT);
                    if (sid[i] < 0) {
                            perror("semget");
                            exit(EXIT_FAILURE);
                    }
            }
            un.val = 0;
            for (i = 0; i < NSET; i++) {
                    for (j = 0; j < NSEM; j++) {
                            if (semctl(sid[i], j, SETVAL, un) < 0)
                                    perror("semctl");
                    }
            }

            /* Launch threads that operate on semaphore set */
            for (i = 0; i < NSEM * NSET * NSET; i++) {
                    p = fork();
                    if (p < 0)
                            perror("fork");
                    if (p == 0)
                            thread();
            }

            /* Free semaphore set */
            for (i = 0; i < NSET; i++) {
                    if (semctl(sid[i], NSEM, IPC_RMID))
                            perror("IPC_RMID");
            }

            /* Wait for forked processes to exit */
            while (wait(NULL)) {
                    if (errno == ECHILD)
                            break;
            };
    }

    int main(int argc, char **argv)
    {
            pid_t p;

            srand(time(NULL));

            while (1) {
                    p = fork();
                    if (p < 0) {
                            perror("fork");
                            exit(EXIT_FAILURE);
                    }
                    if (p == 0) {
                            create_set();
                            goto end;
                    }

                    /* Wait for forked processes to exit */
                    while (wait(NULL)) {
                            if (errno == ECHILD)
                                    break;
                    };
            }
    end:
            return 0;
    }

[akpm@linux-foundation.org: use normal comment layout]
Signed-off-by: NHerton R. Krzesinski <herton@redhat.com>
Acked-by: NManfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Rafael Aquini <aquini@redhat.com>
CC: Aristeu Rozanski <aris@redhat.com>
Cc: David Jeffery <djeffery@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>
      602b8593
  39. 07 8月, 2015 2 次提交
    • S
      ipc: use private shmem or hugetlbfs inodes for shm segments. · e1832f29
      由 Stephen Smalley 提交于 
      The shm implementation internally uses shmem or hugetlbfs inodes for shm
segments.  As these inodes are never directly exposed to userspace and
only accessed through the shm operations which are already hooked by
security modules, mark the inodes with the S_PRIVATE flag so that inode
security initialization and permission checking is skipped.

This was motivated by the following lockdep warning:

  ======================================================
   [ INFO: possible circular locking dependency detected ]
   4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1 Tainted: G        W
  -------------------------------------------------------
   httpd/1597 is trying to acquire lock:
   (&ids->rwsem){+++++.}, at: shm_close+0x34/0x130
   but task is already holding lock:
   (&mm->mmap_sem){++++++}, at: SyS_shmdt+0x4b/0x180
   which lock already depends on the new lock.
   the existing dependency chain (in reverse order) is:
   -> #3 (&mm->mmap_sem){++++++}:
        lock_acquire+0xc7/0x270
        __might_fault+0x7a/0xa0
        filldir+0x9e/0x130
        xfs_dir2_block_getdents.isra.12+0x198/0x1c0 [xfs]
        xfs_readdir+0x1b4/0x330 [xfs]
        xfs_file_readdir+0x2b/0x30 [xfs]
        iterate_dir+0x97/0x130
        SyS_getdents+0x91/0x120
        entry_SYSCALL_64_fastpath+0x12/0x76
   -> #2 (&xfs_dir_ilock_class){++++.+}:
        lock_acquire+0xc7/0x270
        down_read_nested+0x57/0xa0
        xfs_ilock+0x167/0x350 [xfs]
        xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
        xfs_attr_get+0xbd/0x190 [xfs]
        xfs_xattr_get+0x3d/0x70 [xfs]
        generic_getxattr+0x4f/0x70
        inode_doinit_with_dentry+0x162/0x670
        sb_finish_set_opts+0xd9/0x230
        selinux_set_mnt_opts+0x35c/0x660
        superblock_doinit+0x77/0xf0
        delayed_superblock_init+0x10/0x20
        iterate_supers+0xb3/0x110
        selinux_complete_init+0x2f/0x40
        security_load_policy+0x103/0x600
        sel_write_load+0xc1/0x750
        __vfs_write+0x37/0x100
        vfs_write+0xa9/0x1a0
        SyS_write+0x58/0xd0
        entry_SYSCALL_64_fastpath+0x12/0x76
  ...
Signed-off-by: NStephen Smalley <sds@tycho.nsa.gov>
Reported-by: NMorten Stevens <mstevens@fedoraproject.org>
Acked-by: NHugh Dickins <hughd@google.com>
Acked-by: NPaul Moore <paul@paul-moore.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e1832f29
    • M
      ipc: modify message queue accounting to not take kernel data structures into account · de54b9ac
      由 Marcus Gelderie 提交于 
      A while back, the message queue implementation in the kernel was
improved to use btrees to speed up retrieval of messages, in commit
d6629859 ("ipc/mqueue: improve performance of send/recv").

That patch introducing the improved kernel handling of message queues
(using btrees) has, as a by-product, changed the meaning of the QSIZE
field in the pseudo-file created for the queue.  Before, this field
reflected the size of the user-data in the queue.  Since, it also takes
kernel data structures into account.  For example, if 13 bytes of user
data are in the queue, on my machine the file reports a size of 61
bytes.

There was some discussion on this topic before (for example
https://lkml.org/lkml/2014/10/1/115).  Commenting on a th lkml, Michael
Kerrisk gave the following background
(https://lkml.org/lkml/2015/6/16/74):

    The pseudofiles in the mqueue filesystem (usually mounted at
    /dev/mqueue) expose fields with metadata describing a message
    queue. One of these fields, QSIZE, as originally implemented,
    showed the total number of bytes of user data in all messages in
    the message queue, and this feature was documented from the
    beginning in the mq_overview(7) page. In 3.5, some other (useful)
    work happened to break the user-space API in a couple of places,
    including the value exposed via QSIZE, which now includes a measure
    of kernel overhead bytes for the queue, a figure that renders QSIZE
    useless for its original purpose, since there's no way to deduce
    the number of overhead bytes consumed by the implementation.
    (The other user-space breakage was subsequently fixed.)

This patch removes the accounting of kernel data structures in the
queue.  Reporting the size of these data-structures in the QSIZE field
was a breaking change (see Michael's comment above).  Without the QSIZE
field reporting the total size of user-data in the queue, there is no
way to deduce this number.

It should be noted that the resource limit RLIMIT_MSGQUEUE is counted
against the worst-case size of the queue (in both the old and the new
implementation).  Therefore, the kernel overhead accounting in QSIZE is
not necessary to help the user understand the limitations RLIMIT imposes
on the processes.
Signed-off-by: NMarcus Gelderie <redmnic@gmail.com>
Acked-by: NDoug Ledford <dledford@redhat.com>
Acked-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Acked-by: NDavidlohr Bueso <dbueso@suse.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: John Duffy <jb_duffy@btinternet.com>
Cc: Arto Bendiken <arto@bendiken.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      de54b9ac
  41. 01 7月, 2015 6 次提交
  43. 08 5月, 2015 1 次提交
    • D
      ipc/mqueue: Implement lockless pipelined wakeups · fa6004ad
      由 Davidlohr Bueso 提交于 
      This patch moves the wakeup_process() invocation so it is not done under
the info->lock by making use of a lockless wake_q. With this change, the
waiter is woken up once it is STATE_READY and it does not need to loop
on SMP if it is still in STATE_PENDING. In the timeout case we still need
to grab the info->lock to verify the state.

This change should also avoid the introduction of preempt_disable() in -rt
which avoids a busy-loop which pools for the STATE_PENDING -> STATE_READY
change if the waiter has a higher priority compared to the waker.

Additionally, this patch micro-optimizes wq_sleep by using the cheaper
cousin of set_current_state(TASK_INTERRUPTABLE) as we will block no
matter what, thus get rid of the implied barrier.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NGeorge Spelvin <linux@horizon.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Mason <clm@fb.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1430748166.1940.17.camel@stgolabs.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      fa6004ad