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Howlett" Subject: Re: [PATCH v2] mm: fix vma_start_write_killable() signal handling Message-ID: References: <20251126174500.2498895-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: A55EDC0015 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: z3r98wgbyrx5shpwowi41wxixsgemxfd X-HE-Tag: 1764185674-334169 X-HE-Meta: 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 AqG3f2IX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Nov 26, 2025 at 07:53:13PM +0100, Vlastimil Babka wrote: > On 11/26/25 7:43 PM, Suren Baghdasaryan wrote: > > On Wed, Nov 26, 2025 at 6:28 PM Matthew Wilcox wrote: > >> > >> On Wed, Nov 26, 2025 at 06:06:53PM +0000, Lorenzo Stoakes wrote: > >>> On Wed, Nov 26, 2025 at 05:44:58PM +0000, Matthew Wilcox (Oracle) wrote: > >>>> If we get a signal, we need to restore the vm_refcnt. We don't think > >>>> that the refcount can actually be decremented to zero here as it > >>>> requires the VMA to be detached, and the vma_mark_detached() uses > >>>> TASK_UNINTERRUPTIBLE. However, that's a bit subtle, so handle it > >>>> as if the refcount was zero at the start of this function. > >>>> > >>>> Reported-by: syzbot+5b19bad23ac7f44bf8b8@syzkaller.appspotmail.com > > Closes: https://lore.kernel.org/all/69252076.a70a0220.d98e3.009b.GAE@google.com/ > > Unfortunately the reported-by code doesn't work as message id Hm, that seems like a bug in syzbot. The mail it sends doesn't use the word "Closes:" anywhere; it just asks for Reported-by: and Fixes: If that's not enough, then it should also ask for Closes. > >>> Really think we should WARN_ON_ONCE() as Vlasta suggested. > > Thanks Lorenzo! > > Can we at least add a "WARN_ON_ONCE(!detaching);" before "err = 0;". That makes sense; it mirrors the similar calls in the callers of __vma_exit_locked().