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SubjectRe: [PATCH] task_work: add a scheduling point in task_work_run()
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On Tue, 2012-08-21 at 15:05 +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> It seems commit 4a9d4b02 (switch fput to task_work_add) reintroduced
> the problem addressed in commit 944be0b2 (close_files(): add scheduling
> point)
>
> If a server process with a lot of files (say 2 million tcp sockets)
> is killed, we can spend a lot of time in task_work_run() and trigger
> a soft lockup.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
> kernel/task_work.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 91d4e17..d320d44 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -75,6 +75,7 @@ void task_work_run(void)
> p = q->next;
> q->func(q);
> q = p;
> + cond_resched();
> }
> }
> }

We're here, because fput() called schedule_work() to delay the last
fput(). The execution needs to take place before the syscall returns to
userspace. Need to read __schedule()... Do you know if cond_resched()
can guarantee that it will be executed before the return to userspace?

thanks,

Mimi



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