[PATCH] Remove might_sleep from wait_event_cmd

[PATCH] Remove might_sleep from wait_event_cmd

[Mikulas Patocka]

Hi

Please apply this before 3.19 is released.

Mikulas


The patch e22b886a8a43b147e1994a9f970f678fc0df2033 introduced a bug in the
raid5 subsystem.

The function raid5_quiesce (and resize_stripes) calls 
lock_all_device_hash_locks_irq that disables interrupts and takes a few 
spinlocks, then it calls wait_event_cmd with cmd1 
unlock_all_device_hash_locks_irq(conf) and cmd2 
lock_all_device_hash_locks_irq(conf). cmd1 unlocks the spinlocks and 
enables interrupts, cmd2 disables interrupts and locks the spinlock.

The patch e22b886a8a43b147e1994a9f970f678fc0df2033 adds might_sleep() to a
position where spinlocks are taken, thus it introduces a bug.

This patch removes might_sleep() from wait_event_cmd.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 include/linux/wait.h |    1 -
 1 file changed, 1 deletion(-)

Index: linux-2.6/include/linux/wait.h
===================================================================
--- linux-2.6.orig/include/linux/wait.h	2014-12-30 01:19:25.564231262 +0100
+++ linux-2.6/include/linux/wait.h	2015-02-02 15:30:16.766354658 +0100
@@ -363,7 +363,6 @@ do {									\
  */
 #define wait_event_cmd(wq, condition, cmd1, cmd2)			\
 do {									\
-	might_sleep();							\
 	if (condition)							\
 		break;							\
 	__wait_event_cmd(wq, condition, cmd1, cmd2);			\

Re: [PATCH] Remove might_sleep from wait_event_cmd

[NeilBrown]

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On Mon, 2 Feb 2015 09:39:02 -0500 (EST) Mikulas Patocka <mpatocka@redhat.com>
wrote:

> Hi
> 
> Please apply this before 3.19 is released.
> 
> Mikulas
> 
> 
> The patch e22b886a8a43b147e1994a9f970f678fc0df2033 introduced a bug in the
> raid5 subsystem.
> 
> The function raid5_quiesce (and resize_stripes) calls 
> lock_all_device_hash_locks_irq that disables interrupts and takes a few 
> spinlocks, then it calls wait_event_cmd with cmd1 
> unlock_all_device_hash_locks_irq(conf) and cmd2 
> lock_all_device_hash_locks_irq(conf). cmd1 unlocks the spinlocks and 
> enables interrupts, cmd2 disables interrupts and locks the spinlock.
> 
> The patch e22b886a8a43b147e1994a9f970f678fc0df2033 adds might_sleep() to a
> position where spinlocks are taken, thus it introduces a bug.
> 
> This patch removes might_sleep() from wait_event_cmd.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> 
> ---
>  include/linux/wait.h |    1 -
>  1 file changed, 1 deletion(-)
> 
> Index: linux-2.6/include/linux/wait.h
> ===================================================================
> --- linux-2.6.orig/include/linux/wait.h	2014-12-30 01:19:25.564231262 +0100
> +++ linux-2.6/include/linux/wait.h	2015-02-02 15:30:16.766354658 +0100
> @@ -363,7 +363,6 @@ do {									\
>   */
>  #define wait_event_cmd(wq, condition, cmd1, cmd2)			\
>  do {									\
> -	might_sleep();							\
>  	if (condition)							\
>  		break;							\
>  	__wait_event_cmd(wq, condition, cmd1, cmd2);			\
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/


I support this patch.
However in case it doesn't get in, I've queued up a patch to change raid5.c
to use __wait_event_cmd instead...

NeilBrown

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Re: [PATCH] Remove might_sleep from wait_event_cmd

[Peter Zijlstra]

On Tue, Feb 03, 2015 at 09:12:53AM +1100, NeilBrown wrote:
> I support this patch.

It should hopefully already be en-route to tip.

> However in case it doesn't get in, I've queued up a patch to change raid5.c
> to use __wait_event_cmd instead...

So those primitives are useful in their own; their typical use would be
when you already know @cond to be false and want to avoid the extra
invocation.

Re: [PATCH] Remove might_sleep from wait_event_cmd

[NeilBrown]

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On Tue, 3 Feb 2015 12:06:30 +0100 Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Feb 03, 2015 at 09:12:53AM +1100, NeilBrown wrote:
> > I support this patch.
> 
> It should hopefully already be en-route to tip.

Hopefully that means it will be in 3.19-final...

Thanks, I'll drop my __wait_event_cmd patch then.

NeilBrown

> 
> > However in case it doesn't get in, I've queued up a patch to change raid5.c
> > to use __wait_event_cmd instead...
> 
> So those primitives are useful in their own; their typical use would be
> when you already know @cond to be false and want to avoid the extra
> invocation.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/


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[tip:sched/urgent] sched/wait: Remove might_sleep() from wait_event_cmd()

[tip-bot for Mikulas Patocka]

Commit-ID:  3e87523897e18a3e17fc8955ed795188be737ff1
Gitweb:     http://git.kernel.org/tip/3e87523897e18a3e17fc8955ed795188be737ff1
Author:     Mikulas Patocka <mpatocka@redhat.com>
AuthorDate: Mon, 2 Feb 2015 09:39:02 -0500
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 3 Feb 2015 12:14:25 +0100

sched/wait: Remove might_sleep() from wait_event_cmd()

The patch e22b886a8a43 ("sched/wait: Add might_sleep() checks")
introduced a bug in the raid5 subsystem.

The function raid5_quiesce() (and resize_stripes()) uses the 'cmd'
part to release and acquire a spinlock (so we call the sleep
primitives in atomic context), and therefore we cannot do the
might_sleep() check.

Remove it.

Fixes: e22b886a8a43 ("sched/wait: Add might_sleep() checks")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1502020935580.13510@file01.intranet.prod.int.rdu2.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/wait.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2232ed1..37423e0 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -363,7 +363,6 @@ do {									\
  */
 #define wait_event_cmd(wq, condition, cmd1, cmd2)			\
 do {									\
-	might_sleep();							\
 	if (condition)							\
 		break;							\
 	__wait_event_cmd(wq, condition, cmd1, cmd2);			\