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Subject: Re: [PATCH] mm: Replace verify_mm_writelocked() by
 lockdep_assert_held_exclusive()
References: <1544729885-30702-1-git-send-email-longman@redhat.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <f874f3d6-2f84-cd3a-a227-43496d8175a7@suse.cz>
Date: Thu, 13 Dec 2018 20:40:44 +0100
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To: Waiman Long <longman@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Michal Hocko <mhocko@suse.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi <yang.shi@linux.alibaba.com>

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@redhat.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