linux-kernel - Re: [PATCH-v2 1/3] percpu_ida: Make percpu_ida_alloc + callers accept task state bitmask

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Date:	Fri, 24 Jan 2014 16:14:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	kmo@...erainc.com, target-devel <target-devel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH-v2 1/3] percpu_ida: Make percpu_ida_alloc + callers
 accept task state bitmask

On Thu, Jan 23, 2014 at 11:38:24AM -0800, Nicholas A. Bellinger wrote:
> > AFAICT, those changes don't address the original bug that the series was
> > trying to address, allowing the percpu_ida_alloc() tag stealing slow
> > path to be interrupted by a signal..
> > 
> > Also, keep in mind this change needs to be backported to >= v3.12, which
> > is why the percpu_ida changes have been kept to a minimum.

Well, the other option is to revert whatever caused the issue in the
first place :-)

I'm not much for making ugly fixes just because its easier to backport.

> <A little too eager to SEND>
> 
> So would you prefer the following addition to the original bugfix
> instead..?

I'll make a right old mess out of percpu_ida.c, but yeah.

> diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c
> index a48ce2e..58b6714 100644
> --- a/lib/percpu_ida.c
> +++ b/lib/percpu_ida.c
> @@ -174,7 +174,8 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
>                  *
>                  * global lock held and irqs disabled, don't need percpu lock
>                  */
> -               prepare_to_wait(&pool->wait, &wait, state);
> +               if (state != TASK_RUNNING)
> +                       prepare_to_wait(&pool->wait, &wait, state);
>  
>                 if (!tags->nr_free)
>                         alloc_global_tags(pool, tags);
> @@ -199,8 +200,9 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
>                 local_irq_save(flags);
>                 tags = this_cpu_ptr(pool->tag_cpu);
>         }
> +       if (state != TASK_RUNNING)
> +               finish_wait(&pool->wait, &wait);
>  
> -       finish_wait(&pool->wait, &wait);
>         return tag;
>  }
>  EXPORT_SYMBOL_GPL(percpu_ida_alloc);
> 
> 
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