* [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait()
@ 2010-12-20 22:30 Jesper Juhl
2010-12-21 5:54 ` Andrew Morton
2010-12-21 10:30 ` Oleg Nesterov
0 siblings, 2 replies; 3+ messages in thread
From: Jesper Juhl @ 2010-12-20 22:30 UTC (permalink / raw)
To: linux-kernel
Cc: Andrew Morton, Oleg Nesterov, Roland McGrath, Ingo Molnar,
Paul E. McKenney
Hi,
The Coverity checker spotted this. I think it has a point, but I'm not
intimate with this code so there could be somethingI'm missing.
It seems that kernel/exit.c::do_wait() does not always release
'tasklist_lock'. There are multiple ways the code could be changed to make
sure it's always released, I just picked the most straight forward one.
Does this look right to everyone else or is it just me?
I've only compile tested the patch so far.
Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
exit.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 676149a..456b13d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1647,12 +1647,16 @@ repeat:
tsk = current;
do {
retval = do_wait_thread(wo, tsk);
- if (retval)
+ if (retval) {
+ read_unlock(&tasklist_lock);
goto end;
+ }
retval = ptrace_do_wait(wo, tsk);
- if (retval)
+ if (retval) {
+ read_unlock(&tasklist_lock);
goto end;
+ }
if (wo->wo_flags & __WNOTHREAD)
break;
--
Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait()
2010-12-20 22:30 [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait() Jesper Juhl
@ 2010-12-21 5:54 ` Andrew Morton
2010-12-21 10:30 ` Oleg Nesterov
1 sibling, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2010-12-21 5:54 UTC (permalink / raw)
To: Jesper Juhl
Cc: linux-kernel, Oleg Nesterov, Roland McGrath, Ingo Molnar,
Paul E. McKenney
On Mon, 20 Dec 2010 23:30:38 +0100 (CET) Jesper Juhl <jj@chaosbits.net> wrote:
> The Coverity checker spotted this. I think it has a point, but I'm not
> intimate with this code so there could be somethingI'm missing.
>
> It seems that kernel/exit.c::do_wait() does not always release
> 'tasklist_lock'.
do_wait_thread() and ptrace_do_wait() will have released tasklist_lock
if they returned non-zero.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait()
2010-12-20 22:30 [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait() Jesper Juhl
2010-12-21 5:54 ` Andrew Morton
@ 2010-12-21 10:30 ` Oleg Nesterov
1 sibling, 0 replies; 3+ messages in thread
From: Oleg Nesterov @ 2010-12-21 10:30 UTC (permalink / raw)
To: Jesper Juhl
Cc: linux-kernel, Andrew Morton, Roland McGrath, Ingo Molnar,
Paul E. McKenney
On 12/20, Jesper Juhl wrote:
>
> Hi,
>
> The Coverity checker spotted this. I think it has a point, but I'm not
> intimate with this code so there could be somethingI'm missing.
>
> It seems that kernel/exit.c::do_wait() does not always release
> 'tasklist_lock'. There are multiple ways the code could be changed to make
> sure it's always released, I just picked the most straight forward one.
>
> Does this look right to everyone else or is it just me?
> I've only compile tested the patch so far.
>
>
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> ---
> exit.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 676149a..456b13d 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1647,12 +1647,16 @@ repeat:
> tsk = current;
> do {
> retval = do_wait_thread(wo, tsk);
> - if (retval)
> + if (retval) {
> + read_unlock(&tasklist_lock);
No, this is not right.
If wait_consider_task() returns nonzero (pid or errcode), tasklist_lock
should be already released.
That is why, for example, wait_task_stopped() does BUG_ON(!retval) after
it drops tasklist.
Oleg.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2010-12-21 10:37 UTC | newest]
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2010-12-20 22:30 [PATCH][RFC] Always unlock 'tasklist_lock' in kernel/exit.c::do_wait() Jesper Juhl
2010-12-21 5:54 ` Andrew Morton
2010-12-21 10:30 ` Oleg Nesterov
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