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Mon, 23 Mar 2026 22:53:38 -0700 (PDT) Received: from KASONG-MC4 ([43.132.141.21]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b083516194sm128476465ad.4.2026.03.23.22.53.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 22:53:38 -0700 (PDT) Date: Tue, 24 Mar 2026 13:53:33 +0800 From: Kairui Song To: Youngjun Park Cc: "Rafael J . Wysocki" , Andrew Morton , Chris Li , Kairui Song , Pavel Machek , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Usama Arif , linux-pm@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 1/2] mm/swap, PM: hibernate: fix swapoff race in uswsusp by pinning swap device Message-ID: References: <20260323160822.1409904-1-youngjun.park@lge.com> <20260323160822.1409904-2-youngjun.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260323160822.1409904-2-youngjun.park@lge.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 452D0180003 X-Stat-Signature: jca6dcrm5efbr96kgn1pfpm6aetc551y X-Rspam-User: X-HE-Tag: 1774331620-838621 X-HE-Meta: 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 w2yPIcQC MpFvjRvwPuwI3PnLvmv0ysZx2TdbOWs8HCm9J0qGPYuRkcE5y7VZTclo9sDLuJO7wcWGMcUruueDQSlsWH+9Cwr2y3J5olGIP+pKXr7oUfDeYBgySh9q+TBvPG8Wg24yyZqMgzQWcrlhl7S9Q0i1SkipnF3z7TX8DUC1/ixvVptZPx4/2a0lmX6B4ZZZw/jJHOICo55yhgXj/SruvelR4X4FHmdu3bszq9Rp/Z+cX+KbA9NvLFEGLeO2EyFNErC7xLhcoHAmteb2/TKwAqdRq3b2Yu/LwZBL63AVs0VbPdFlNTKkM7SMuhYLb2W7o71xZ4ovGMU6q5E1suVMQGZjjioITHS/pplmuXJr81WiHxITQgZlojiKBmv/CX/7PH/T2tVu21uUiNqvz4vjCXJlP3s9H3yx7F5bcikcwPd7iU9MZy36UFQgBa6FDB3FzYDKFeJdLNd5JyTlWPJc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 01:08:21AM +0800, Youngjun Park wrote: > Hibernation via uswsusp (/dev/snapshot ioctls) has a race window: > after selecting the resume swap area but before user space is frozen, > swapoff may run and invalidate the selected swap device. > > Fix this by pinning the swap device with SWP_HIBERNATION while it is > in use. The pin is exclusive, which is sufficient since > hibernate_acquire() already prevents concurrent hibernation sessions. > > The kernel swsusp path (sysfs-based hibernate/resume) uses > find_hibernation_swap_type() which is not affected by the pin. It > freezes user space before touching swap, so swapoff cannot race. > > Introduce dedicated helpers: > - pin_hibernation_swap_type(): Look up and pin the swap device. > Used by the uswsusp path. > - find_hibernation_swap_type(): Lookup without pinning. > Used by the kernel swsusp path. > - unpin_hibernation_swap_type(): Clear the hibernation pin. Looks good to me, thanks! Reviewed-by: Kairui Song Just one trivial nit picks below. > +/** > + * unpin_hibernation_swap_type - Unpin the swap device for hibernation > + * @type: Swap type previously returned by pin_hibernation_swap_type() > + * > + * Clear the hibernation pin on the given swap device, allowing > + * swapoff() to proceed normally. > + * > + * If @type does not refer to a valid swap device, this function > + * does nothing. > + */ > +void unpin_hibernation_swap_type(int type) > +{ > + struct swap_info_struct *si; > + > + spin_lock(&swap_lock); > + si = swap_type_to_info(type); > + if (!si) { > + spin_unlock(&swap_lock); > + return; > + } > + si->flags &= ~SWP_HIBERNATION; Will the code will be simpler if you just: if (si) si->flags &= ~SWP_HIBERNATION; Just personal taste, free feel to ignore. And as you mentioned this is on top of swap table p3 so you based it on mm-new - but isn't p3 already in mm-unstable? Maybe we can have it there? Not sure how much conflict are there with PM. The code and design looks OK.