linux-kernel - Re: [BUG] mm/vmalloc: ___might_sleep is called under a spinlock in __purge_vmap_area

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Date:   Mon, 9 Oct 2017 07:10:01 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Jia-Ju Bai <baijiaju1990@....com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com, mingo@...nel.org,
        catalin.marinas@....com, labbott@...hat.com, thgarnie@...gle.com,
        kirill.shutemov@...ux.intel.com, aryabinin@...tuozzo.com,
        ard.biesheuvel@...aro.org, zijun_hu@....com, linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] mm/vmalloc: ___might_sleep is called under a spinlock in
 __purge_vmap_area_lazy

On Mon, Oct 09, 2017 at 12:00:33PM +0800, Jia-Ju Bai wrote:
> The ___might_sleep is called under a spinlock, and the function call graph
> is:
> __purge_vmap_area_lazy (acquire the spinlock)
>   cond_resched_lock
>     ___might_sleep
> 
> In this situation, ___might_sleep may prints error log message because a
> spinlock is held.
> A possible fix is to remove ___might_sleep in cond_resched_lock.
> 
> This bug is found by my static analysis tool and my code review.

This analysis doesn't makes sense.

The point of cond_resched_lock() is that it drops the lock, if resched is
required.

___might_sleep() is called with preempt_offset equal to
PREEMPT_LOCK_OFFSET, so it won't report error if it's the only lock we
hold.

-- 
 Kirill A. Shutemov