From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 73B7636E495; Fri, 20 Mar 2026 08:12:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773994365; cv=none; b=S/mbC6bhykpQlN+QexwozhBx4dzfjiAqNnhYZQ/LvB4I74/deNUUS7CMtb8siIZLFq7/qwTTGB30O4tjXUE7V4EQ+hBmS5g1n7c3sE32fQoWOe2NDdL++Cr/jPWcYZPEf0mJ9LC0nkEiLvwOBCYg+N9M25xG2VhZWFH+1p/fPXk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773994365; c=relaxed/simple; bh=bKDVCqTM4J91R7IvMYDkjFY61oGEb/tt+7PlrQhX1HY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BVTCgBpvmvRMaphJp5gYlHMDGmvt0Dc9+7EHOula1IajuktLDlDg9cNXsKJSSMIHEkSclNwPogJAg8BxTPs6KK/GJgvQuymgTn91MJViR9DVp4mY5HiSTa0TkukZTQHpjEnmNqsYSTQXoOs+SuX4UBFCZB64IA6+ryFiQFn1y+E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=azx31kU0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="azx31kU0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15121C4CEF7; Fri, 20 Mar 2026 08:12:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773994365; bh=bKDVCqTM4J91R7IvMYDkjFY61oGEb/tt+7PlrQhX1HY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=azx31kU0gP1cqkljdCivld5BsJa95qVMQh0lUqLWpwrSMVzC2J72H2av1f4l4OroJ hESw43ZLGLNK27gM/HGW5NMGekELE+7CjOhCzhW4/IBAqijq0LSdY1IHr25cHLGwSu OdBveZ6tjzl+f1RPJGO1Lc1jO7cvjxLgQlc1yr6F/3/hFfN0BR48timtKsoUK+5t2I MGL2a4XEStrkdCzdfDbbpaDERiYXjoofeBzC+TVzIwWwMwELdPSaQMAZNmzUYMGRg0 MCvP+/YXSeYMFwyh+Q8bh36GXV2N4Unra84tj2POH4z8zr53zG4kZ0jsZO/refPOlV UUSDh6J4oKC5w== Message-ID: Date: Fri, 20 Mar 2026 09:12:41 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/1] writeback: don't block sync for filesystems with no data integrity guarantees To: Joanne Koong , brauner@kernel.org Cc: linux-fsdevel@vger.kernel.org, jack@suse.cz, miklos@szeredi.hu, therealgraysky@proton.me, linux-pm@vger.kernel.org, stable@vger.kernel.org References: <20260320005145.2483161-1-joannelkoong@gmail.com> <20260320005145.2483161-2-joannelkoong@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/20/26 01:51, Joanne Koong wrote: > Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot > guarantee data persistence on sync (eg fuse). For superblocks with this > flag set, sync kicks off writeback of dirty inodes but does not wait > for the flusher threads to complete the writeback. > > This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in > commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings > in wait_sb_inodes()"). The flag belongs at the superblock level because > data integrity is a filesystem-wide property, not a per-inode one. > Having this flag at the superblock level also allows us to skip having > to iterate every dirty inode in wait_sb_inodes() only to skip each inode > individually. > > Prior to this commit, mappings with no data integrity guarantees skipped > waiting on writeback completion but still waited on the flusher threads > to finish initiating the writeback. Waiting on the flusher threads is > unnecessary. This commit kicks off writeback but does not wait on the > flusher threads. This change properly addresses a recent report [1] for > a suspend-to-RAM hang seen on fuse-overlayfs that was caused by waiting > on the flusher threads to finish: > > Workqueue: pm_fs_sync pm_fs_sync_work_fn > Call Trace: > > __schedule+0x457/0x1720 > schedule+0x27/0xd0 > wb_wait_for_completion+0x97/0xe0 > sync_inodes_sb+0xf8/0x2e0 > __iterate_supers+0xdc/0x160 > ksys_sync+0x43/0xb0 > pm_fs_sync_work_fn+0x17/0xa0 > process_one_work+0x193/0x350 > worker_thread+0x1a1/0x310 > kthread+0xfc/0x240 > ret_from_fork+0x243/0x280 > ret_from_fork_asm+0x1a/0x30 > > > On fuse this is problematic because there are paths that may cause the > flusher thread to block (eg if systemd freezes the user session cgroups > first, which freezes the fuse daemon, before invoking the kernel > suspend. The kernel suspend triggers ->write_node() which on fuse issues > a synchronous setattr request, which cannot be processed since the > daemon is frozen. Or if the daemon is buggy and cannot properly complete > writeback, initiating writeback on a dirty folio already under writeback > leads to writeback_get_folio() -> folio_prepare_writeback() -> > unconditional wait on writeback to finish, which will cause a hang). > This commit restores fuse to its prior behavior before tmp folios were > removed, where sync was essentially a no-op. > > [1] https://lore.kernel.org/linux-fsdevel/CAJnrk1a-asuvfrbKXbEwwDSctvemF+6zfhdnuzO65Pt8HsFSRw@mail.gmail.com/T/#m632c4648e9cafc4239299887109ebd880ac6c5c1 > > Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") > Reported-by: John > Cc: > Signed-off-by: Joanne Koong > --- Looks reasonable to me. With my little experience in fs land: Reviewed-by: David Hildenbrand (Arm) -- Cheers, David