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Wysocki" , Pavel Machek , Len Brown , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [PATCH] mm/swap, PM: hibernate: atomically replace hibernation pin Message-Id: <20260501061816.5d59d1eefb0a41a3480a3a11@linux-foundation.org> In-Reply-To: <20260430195651.287659-1-devnexen@gmail.com> References: <20260430195651.287659-1-devnexen@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A5EBB12001C X-Rspamd-Server: rspam04 X-Stat-Signature: 5umef163w43qumuyu5uyex81cqxxk3dq X-HE-Tag: 1777641498-384895 X-HE-Meta: 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 3vDp7mWR Uf6gFnBWoYImHRWfpu2FvSLzoH9X8lgfE9bmM81QFYAjxniElLgcnMfmimuqmoQi7R9g56ohJ36nZxYVLaommWCNcXY9AJB/EnBl6J2c7MMmNLJrAv5YsmT0beP64APXqaGkQ2WfrvJ3E3U0jzq+E8KLgwIU7h9pAw8zpwLj0NhFQImAF+GkJiRt+z+qCvWaZzBe8DbyNM3FCJEQudJLqMgdiRFIO1DimnFkyzWK/ExBTb0tJv5HBfyXP/M7kw9O5BnmGSAMz2PW55t7soYTpj58kXQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 30 Apr 2026 20:56:51 +0100 David Carlier wrote: > snapshot_set_swap_area() unpins the previously selected swap device > and pins the new one in two separate swap_lock critical sections. > In the gap between them, swapoff() observes SWP_HIBERNATION cleared, > bypasses the guard, and tears down the device, reopening the race > the SWP_HIBERNATION pin was meant to close. The window is reachable > on any SNAPSHOT_SET_SWAP_AREA call after the snapshot device is > opened for hibernation, and on any retry after the resume path's > first selection. > > Add repin_hibernation_swap_type(), which looks up the new device, > clears the old SWP_HIBERNATION flag and sets the new one under a > single swap_lock acquisition. The same-device case is short- > circuited so userspace can re-select the same swap area without > tripping WARN_ON_ONCE and -EBUSY. Switch snapshot_set_swap_area() > to the new helper. > > A failed lookup now preserves the previous pin instead of dropping > it, so a bad SNAPSHOT_SET_SWAP_AREA leaves the prior selection > intact. The open and release paths keep using > pin_hibernation_swap_type() and unpin_hibernation_swap_type(). > > The race was identified during AI-assisted review of the > SWP_HIBERNATION pinning series. Thanks, I'll queue this for testing. Can the swap maintainers please do a detailed review at some point?