From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jann Horn <jannh@google.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
linux-mm@kvack.org, "John Hubbard" <jhubbard@nvidia.com>,
"Christoph Hellwig" <hch@lst.de>,
linux-kernel@vger.kernel.org,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH] mm/mmu_notifier: Fix mmget() assert in __mmu_interval_notifier_insert
Date: Mon, 31 Aug 2020 21:26:34 -0300 [thread overview]
Message-ID: <20200901002634.GD24045@ziepe.ca> (raw)
In-Reply-To: <20200901000143.207585-1-jannh@google.com>
On Tue, Sep 01, 2020 at 02:01:43AM +0200, Jann Horn wrote:
> The comment talks about having to hold mmget() (which means mm_users), but
> the actual check is on mm_count (which would be mmgrab()).
>
> Given that MMU notifiers are torn down in
> mmput() -> __mmput() -> exit_mmap() -> mmu_notifier_release(),
> I believe that the comment is correct and the check should be on
> mm->mm_users. Fix it up accordingly.
>
> Fixes: 99cb252f5e68 ("mm/mmu_notifier: add an interval tree notifier")
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> Can someone please double-check this? I'm like 90% sure that I fixed
> this the right way around, but it'd be good if someone more familiar
> with mmu notifiers could confirm.
Hmm.. I added the comment but copied the expression from older code.
The intent is certainly that the caller must have a mmget, this
function must not race with __mmu_notifier_release() and the mmget is
what prevents that.
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Jason
prev parent reply other threads:[~2020-09-01 0:26 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 0:01 [PATCH] mm/mmu_notifier: Fix mmget() assert in __mmu_interval_notifier_insert Jann Horn
2020-09-01 0:26 ` Jason Gunthorpe [this message]
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