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b=NVOEmJQIcpmi+K/sq7V/gYq7ISiAHCfwFLxSVr0Rdazw0dZdxIK3LmfK2xqRS5IbXH1BxM dQzlX75l0xa4JcAA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 7F8DF136E6; Wed, 2 Sep 2026 12:43:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id gc2cHtQZmGoKKgAAD6G6ig (envelope-from ); Wed, 02 Sep 2026 12:43:00 +0000 Message-ID: <676f40aa-2804-4f5b-b0d6-a5f95984601d@suse.de> Date: Wed, 2 Sep 2026 14:43:00 +0200 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/7] block: use iomap_dirty_folio for block devices To: Tal Zussman , Jens Axboe , Christoph Hellwig , Johannes Thumshirn , Luis Chamberlain , "Matthew Wilcox (Oracle)" , John Garry , Christian Brauner , "Darrick J. Wong" , Keith Busch , "Martin K. Petersen" Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko References: <20260828-blkdev-fixes-v2-0-32f3f40cebed@columbia.edu> <20260828-blkdev-fixes-v2-1-32f3f40cebed@columbia.edu> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20260828-blkdev-fixes-v2-1-32f3f40cebed@columbia.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Level: X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Queue-Id: B87DE21A41 X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,sashiko.dev:url,suse.de:dkim,suse.de:email,suse.de:mid]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Flag: NO X-Spam-Score: -4.51 On 8/28/26 3:49 PM, Tal Zussman wrote: > With CONFIG_BUFFER_HEAD=n, block devices are written back through iomap, > but def_blk_aops uses filemap_dirty_folio, which only sets PG_dirty. It > does not set the per-block dirty bits in the folio's iomap_folio_state, > so iomap_writeback_folio() finds no dirty range, submits no I/O and > clears PG_dirty, resulting in data loss. > > Other iomap users set .dirty_folio to iomap_dirty_folio, which marks the > folio's blocks dirty before calling filemap_dirty_folio(). > > This is only observable with block size < folio size. With a single > block there is no iomap_folio_state to get out of sync and > iomap_writeback_folio() marks the whole folio dirty itself. For a > page-aligned device, this may require using the BLKBSZSET ioctl to set > the block size, which requires CAP_SYS_ADMIN. A device whose size is not > page aligned already gets a sub-page block size from > set_init_blocksize(), so no ioctl and no privilege is needed. > > To reproduce, on a device with a sub-page block size, write a known > pattern with O_DIRECT, mmap the same range, store to it, msync() and > fsync(), then read it back with O_DIRECT. A reproducer is available at > [1]. > > [1] https://gist.github.com/tzussman/18ab05cba4b3fdc79cce0a69d1fd05b4 > > Fixes: 925c86a19bac ("fs: add CONFIG_BUFFER_HEAD") > Reported-by: Sashiko > Link: https://sashiko.dev/#/patchset/20260730-blk-dontcache-v7-0-3e8e6850068d%40columbia.edu?part=5 > Reviewed-by: Christoph Hellwig > Signed-off-by: Tal Zussman > --- > block/fops.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich