linux-kernel - Re: [PATCH] mm: Replace verify_mm_writelocked() by lockdep_assert_held

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Message-ID: <f874f3d6-2f84-cd3a-a227-43496d8175a7@suse.cz>
Date:   Thu, 13 Dec 2018 20:40:44 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH] mm: Replace verify_mm_writelocked() by
 lockdep_assert_held_exclusive()

On 12/13/18 8:38 PM, Waiman Long wrote:
> Using down_read_trylock() to check if a task holds a write lock on
> a rwsem is not reliable. A task can hold a read lock on a rwsem and
> down_read_trylock() can fail if a writer is waiting in the wait queue.
>
> So use lockdep_assert_held_exclusive() instead which can do the right
> check when CONFIG_LOCKDEP is on.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>

There's already a patch in mmotm removing this completely:
https://www.ozlabs.org/~akpm/mmots/broken-out/mm-mmap-remove-verify_mm_writelocked.patch

Vlastimil