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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1swjNt-0000000AbyT-3pxw; Fri, 04 Oct 2024 14:34:21 +0000 Date: Fri, 4 Oct 2024 15:34:21 +0100 From: Matthew Wilcox To: Jeongjun Park Cc: akpm@linux-foundation.org, kasong@tencent.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+fa43f1b63e3aa6f66329@syzkaller.appspotmail.com Subject: Re: [PATCH] mm: swap: prevent possible data-race in __try_to_reclaim_swap Message-ID: References: <20241004142504.4379-1-aha310510@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241004142504.4379-1-aha310510@gmail.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0968F80007 X-Stat-Signature: zn1uk6prrn8w9taqdr43owofi9b6r6ow X-Rspam-User: X-HE-Tag: 1728052471-430509 X-HE-Meta: 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 6OYwKb3/ 29PCND9UN84jHtB/y9wXWwQhq4lxuRxjFQgEy45vSocFEnNrMMCjls4I1m1/Acc2r5RnpgijNhU7HGo2BcAsJJm8nt9cDqLw8igO1v1ilBRs4yppCvsbcMc6jLmtX6eIVNryG/l824but8C/0qlpI4Tyg2QsAlOFmvdMxuO7cdLVxpEAZzKRQkf5f1UiTXhcwX2zLsDjHH6P7KB0fSHsucreOfKDuzdWZwWZ0JUiWV8Wra5pUWXiA5iDL26uSCmQqthTkqfAij4CSgd5V1Y1K9cC0ar7ETc7B7J2cppeQywQ7xbSQsHtk+dlVU+MqT9yi1vTgGzg/h5iX6upGYfqOwVIstxRjJKEHS2KSENs9UUvO8T1x5hzt/T3ynw== 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 Fri, Oct 04, 2024 at 11:25:04PM +0900, Jeongjun Park wrote: > A report [1] was uploaded from syzbot. > > In the previous commit 862590ac3708 ("mm: swap: allow cache reclaim to skip > slot cache"), the __try_to_reclaim_swap() function reads offset and nr_pages > from folio without folio_lock protection. Umm. You don't need folio_lock to read nr_pages. Holding a refcount is sufficient to stabilise nr_pages. I cannot speak to folio->swap though (and the KCSAN report does appear to be pointing to folio->swap).