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  1. 26 7月, 2008 1 次提交
    • O
      kill PF_BORROWED_MM in favour of PF_KTHREAD · 246bb0b1
      由 Oleg Nesterov 提交于 
      Kill PF_BORROWED_MM.  Change use_mm/unuse_mm to not play with ->flags, and
do s/PF_BORROWED_MM/PF_KTHREAD/ for a couple of other users.

No functional changes yet.  But this allows us to do further
fixes/cleanups.

oom_kill/ptrace/etc often check "p->mm != NULL" to filter out the
kthreads, this is wrong because of use_mm().  The problem with
PF_BORROWED_MM is that we need task_lock() to avoid races.  With this
patch we can check PF_KTHREAD directly, or use a simple lockless helper:

	/* The result must not be dereferenced !!! */
	struct mm_struct *__get_task_mm(struct task_struct *tsk)
	{
		if (tsk->flags & PF_KTHREAD)
			return NULL;
		return tsk->mm;
	}

Note also ecard_task().  It runs with ->mm != NULL, but it's the kernel
thread without PF_BORROWED_MM.
Signed-off-by: NOleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      246bb0b1
  3. 07 6月, 2008 1 次提交
  5. 30 4月, 2008 1 次提交
  7. 29 4月, 2008 3 次提交
  9. 28 4月, 2008 1 次提交
  11. 11 4月, 2008 2 次提交
  13. 20 3月, 2008 1 次提交
    • Q
      aio: bad AIO race in aio_complete() leads to process hang · 6cb2a210
      由 Quentin Barnes 提交于 
      My group ran into a AIO process hang on a 2.6.24 kernel with the process
sleeping indefinitely in io_getevents(2) waiting for the last wakeup to come
and it never would.

We ran the tests on x86_64 SMP.  The hang only occurred on a Xeon box
("Clovertown") but not a Core2Duo ("Conroe").  On the Xeon, the L2 cache isn't
shared between all eight processors, but is L2 is shared between between all
two processors on the Core2Duo we use.

My analysis of the hang is if you go down to the second while-loop
in read_events(), what happens on processor #1:
	1) add_wait_queue_exclusive() adds thread to ctx->wait
	2) aio_read_evt() to check tail
	3) if aio_read_evt() returned 0, call [io_]schedule() and sleep

In aio_complete() with processor #2:
	A) info->tail = tail;
	B) waitqueue_active(&ctx->wait)
	C) if waitqueue_active() returned non-0, call wake_up()

The way the code is written, step 1 must be seen by all other processors
before processor 1 checks for pending events in step 2 (that were recorded by
step A) and step A by processor 2 must be seen by all other processors
(checked in step 2) before step B is done.

The race I believed I was seeing is that steps 1 and 2 were
effectively swapped due to the __list_add() being delayed by the L2
cache not shared by some of the other processors.  Imagine:
proc 2: just before step A
proc 1, step 1: adds to ctx->wait, but is not visible by other processors yet
proc 1, step 2: checks tail and sees no pending events
proc 2, step A: updates tail
proc 1, step 3: calls [io_]schedule() and sleeps
proc 2, step B: checks ctx->wait, but sees no one waiting, skips wakeup
                so proc 1 sleeps indefinitely

My patch adds a memory barrier between steps A and B.  It ensures that the
update in step 1 gets seen on processor 2 before continuing.  If processor 1
was just before step 1, the memory barrier makes sure that step A (update
tail) gets seen by the time processor 1 makes it to step 2 (check tail).

Before the patch our AIO process would hang virtually 100% of the time.  After
the patch, we have yet to see the process ever hang.
Signed-off-by: NQuentin Barnes <qbarnes+linux@yahoo-inc.com>
Reviewed-by: NZach Brown <zach.brown@oracle.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: <stable@kernel.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
[ We should probably disallow that "if (waitqueue_active()) wake_up()"
  coding pattern, because it's so often buggy wrt memory ordering ]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6cb2a210
  15. 09 2月, 2008 3 次提交
  17. 30 1月, 2008 1 次提交
  19. 06 12月, 2007 1 次提交
  21. 19 10月, 2007 1 次提交
  23. 17 10月, 2007 1 次提交
  25. 09 10月, 2007 1 次提交
  27. 11 5月, 2007 1 次提交
    • D
      signal/timer/event: KAIO eventfd support example · 9c3060be
      由 Davide Libenzi 提交于 
      This is an example about how to add eventfd support to the current KAIO code,
in order to enable KAIO to post readiness events to a pollable fd (hence
compatible with POSIX select/poll).  The KAIO code simply signals the eventfd
fd when events are ready, and this triggers a POLLIN in the fd.  This patch
uses a reserved for future use member of the struct iocb to pass an eventfd
file descriptor, that KAIO will use to post events every time a request
completes.  At that point, an aio_getevents() will return the completed result
to a struct io_event.  I made a quick test program to verify the patch, and it
runs fine here:

http://www.xmailserver.org/eventfd-aio-test.c

The test program uses poll(2), but it'd, of course, work with select and epoll
too.

This can allow to schedule both block I/O and other poll-able devices
requests, and wait for results using select/poll/epoll.  In a typical
scenario, an application would submit KAIO request using aio_submit(), and
will also use epoll_ctl() on the whole other class of devices (that with the
addition of signals, timers and user events, now it's pretty much complete),
and then would:

	epoll_wait(...);
	for_each_event {
		if (curr_event_is_kaiofd) {
			aio_getevents();
			dispatch_aio_events();
		} else {
			dispatch_epoll_event();
		}
	}
Signed-off-by: NDavide Libenzi <davidel@xmailserver.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9c3060be
  29. 10 5月, 2007 2 次提交
  31. 08 5月, 2007 1 次提交
  33. 28 3月, 2007 1 次提交
  35. 12 2月, 2007 2 次提交
  37. 04 2月, 2007 1 次提交
    • K
      [PATCH] aio: fix buggy put_ioctx call in aio_complete - v2 · dee11c23
      由 Ken Chen 提交于 
      An AIO bug was reported that sleeping function is being called in softirq
context:

BUG: warning at kernel/mutex.c:132/__mutex_lock_common()
Call Trace:
     [<a000000100577b00>] __mutex_lock_slowpath+0x640/0x6c0
     [<a000000100577ba0>] mutex_lock+0x20/0x40
     [<a0000001000a25b0>] flush_workqueue+0xb0/0x1a0
     [<a00000010018c0c0>] __put_ioctx+0xc0/0x240
     [<a00000010018d470>] aio_complete+0x2f0/0x420
     [<a00000010019cc80>] finished_one_bio+0x200/0x2a0
     [<a00000010019d1c0>] dio_bio_complete+0x1c0/0x200
     [<a00000010019d260>] dio_bio_end_aio+0x60/0x80
     [<a00000010014acd0>] bio_endio+0x110/0x1c0
     [<a0000001002770e0>] __end_that_request_first+0x180/0xba0
     [<a000000100277b90>] end_that_request_chunk+0x30/0x60
     [<a0000002073c0c70>] scsi_end_request+0x50/0x300 [scsi_mod]
     [<a0000002073c1240>] scsi_io_completion+0x200/0x8a0 [scsi_mod]
     [<a0000002074729b0>] sd_rw_intr+0x330/0x860 [sd_mod]
     [<a0000002073b3ac0>] scsi_finish_command+0x100/0x1c0 [scsi_mod]
     [<a0000002073c2910>] scsi_softirq_done+0x230/0x300 [scsi_mod]
     [<a000000100277d20>] blk_done_softirq+0x160/0x1c0
     [<a000000100083e00>] __do_softirq+0x200/0x240
     [<a000000100083eb0>] do_softirq+0x70/0xc0

See report: http://marc.theaimsgroup.com/?l=linux-kernel&m=116599593200888&w=2

flush_workqueue() is not allowed to be called in the softirq context.
However, aio_complete() called from I/O interrupt can potentially call
put_ioctx with last ref count on ioctx and triggers bug.  It is simply
incorrect to perform ioctx freeing from aio_complete.

The bug is trigger-able from a race between io_destroy() and aio_complete().
A possible scenario:

cpu0                               cpu1
io_destroy                         aio_complete
  wait_for_all_aios {                __aio_put_req
     ...                                 ctx->reqs_active--;
     if (!ctx->reqs_active)
        return;
  }
  ...
  put_ioctx(ioctx)

                                     put_ioctx(ctx);
                                        __put_ioctx
                                          bam! Bug trigger!

The real problem is that the condition check of ctx->reqs_active in
wait_for_all_aios() is incorrect that access to reqs_active is not
being properly protected by spin lock.

This patch adds that protective spin lock, and at the same time removes
all duplicate ref counting for each kiocb as reqs_active is already used
as a ref count for each active ioctx.  This also ensures that buggy call
to flush_workqueue() in softirq context is eliminated.
Signed-off-by: N"Ken Chen" <kenchen@google.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Suparna Bhattacharya <suparna@in.ibm.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: <stable@kernel.org>
Acked-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      dee11c23
  39. 31 12月, 2006 1 次提交
    • Z
      [PATCH] Fix lock inversion aio_kick_handler() · 1ebb1101
      由 Zach Brown 提交于 
      lockdep found a AB BC CA lock inversion in retry-based AIO:

1) The task struct's alloc_lock (A) is acquired in process context with
   interrupts enabled.  An interrupt might arrive and call wake_up() which
   grabs the wait queue's q->lock (B).

2) When performing retry-based AIO the AIO core registers
   aio_wake_function() as the wake funtion for iocb->ki_wait.  It is called
   with the wait queue's q->lock (B) held and then tries to add the iocb to
   the run list after acquiring the ctx_lock (C).

3) aio_kick_handler() holds the ctx_lock (C) while acquiring the
   alloc_lock (A) via lock_task() and unuse_mm().  Lockdep emits a warning
   saying that we're trying to connect the irq-safe q->lock to the
   irq-unsafe alloc_lock via ctx_lock.

This fixes the inversion by calling unuse_mm() in the AIO kick handing path
after we've released the ctx_lock.  As Ben LaHaise pointed out __put_ioctx
could set ctx->mm to NULL, so we must only access ctx->mm while we have the
lock.
Signed-off-by: NZach Brown <zach.brown@oracle.com>
Signed-off-by: NSuparna Bhattacharya <suparna@in.ibm.com>
Acked-by: NBenjamin LaHaise <bcrl@kvack.org>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      1ebb1101
  41. 14 12月, 2006 1 次提交
    • J
      [PATCH] Use activate_mm() in fs/aio.c:use_mm() · 90aef12e
      由 Jeremy Fitzhardinge 提交于 
      activate_mm() is not the right thing to be using in use_mm().  It should be
switch_mm().

On normal x86, they're synonymous, but for the Xen patches I'm adding a
hook which assumes that activate_mm is only used the first time a new mm
is used after creation (I have another hook for dealing with dup_mm).  I
think this use of activate_mm() is the only place where it could be used
a second time on an mm.

>From a quick look at the other architectures I think this is OK (most
simply implement one in terms of the other), but some are doing some
subtly different stuff between the two.
Acked-by: NDavid Miller <davem@davemloft.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      90aef12e
  43. 08 12月, 2006 3 次提交
  45. 30 11月, 2006 1 次提交
  47. 22 11月, 2006 2 次提交
    • D
      WorkStruct: Pass the work_struct pointer instead of context data · 65f27f38
      由 David Howells 提交于 
      Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.

For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.

To make this work, an extra flag is introduced into the management side of the
work_struct.  This governs auto-release of the structure upon execution.

Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function.  This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated..  This is a
problem if the auxiliary data is taken away (as done by the last patch).

However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems.  But then the work function must itself release the
work_struct by calling work_release().

In most cases, automatic release is fine, so this is the default.  Special
initiators exist for the non-auto-release case (ending in _NAR).
Signed-Off-By: NDavid Howells <dhowells@redhat.com>
      65f27f38
    • D
      WorkStruct: Separate delayable and non-delayable events. · 52bad64d
      由 David Howells 提交于 
      Separate delayable work items from non-delayable work items be splitting them
into a separate structure (delayed_work), which incorporates a work_struct and
the timer_list removed from work_struct.

The work_struct struct is huge, and this limits it's usefulness.  On a 64-bit
architecture it's nearly 100 bytes in size.  This reduces that by half for the
non-delayable type of event.
Signed-Off-By: NDavid Howells <dhowells@redhat.com>
      52bad64d
  49. 03 10月, 2006 1 次提交
  51. 01 10月, 2006 2 次提交
  53. 27 6月, 2006 1 次提交
  55. 23 6月, 2006 1 次提交
  57. 26 3月, 2006 1 次提交