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Thu, 8 Aug 2024 16:16:14 +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 5/ISAk7vtGY7KQAAD6G6ig (envelope-from ); Thu, 08 Aug 2024 16:16:14 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 93A88A0851; Thu, 8 Aug 2024 18:16:09 +0200 (CEST) Date: Thu, 8 Aug 2024 18:16:09 +0200 From: Jan Kara To: Ted Tso Cc: linux-ext4@vger.kernel.org, Christian Brauner , linux-fsdevel@vger.kernel.org, Jan Kara Subject: Re: [PATCH] ext4: don't set SB_RDONLY after filesystem errors Message-ID: <20240808161609.xntlkgsglosowndg@quack3> References: <20240805201241.27286-1-jack@suse.cz> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240805201241.27286-1-jack@suse.cz> X-Spam-Level: X-Spamd-Result: default: False [-0.80 / 50.00]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; URIBL_BLOCKED(0.00)[suse.com:email,suse.cz:email,imap1.dmz-prg2.suse.org:helo]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_TLS_LAST(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:email,suse.com:email] X-Spam-Flag: NO X-Spam-Score: -0.80 On Mon 05-08-24 22:12:41, Jan Kara wrote: > When the filesystem is mounted with errors=remount-ro, we were setting > SB_RDONLY flag to stop all filesystem modifications. We knew this misses > proper locking (sb->s_umount) and does not go through proper filesystem > remount procedure but it has been the way this worked since early ext2 > days and it was good enough for catastrophic situation damage > mitigation. Recently, syzbot has found a way (see link) to trigger > warnings in filesystem freezing because the code got confused by > SB_RDONLY changing under its hands. Since these days we set > EXT4_FLAGS_SHUTDOWN on the superblock which is enough to stop all > filesystem modifications, modifying SB_RDONLY shouldn't be needed. So > stop doing that. > > Link: https://lore.kernel.org/all/000000000000b90a8e061e21d12f@google.com > Reported-by: Christian Brauner > Signed-off-by: Jan Kara > --- > fs/ext4/super.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > Note that this patch introduces fstests failure with generic/459 test > because it assumes that either freezing succeeds or 'ro' is among mount > options. But we fail the freeze with EFSCORRUPTED. This needs fixing in > the test but at this point I'm not sure how exactly. OK, I have noticed that recent versions of fstests have the check already improved and so generic/459 passes with these changes. Honza > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > index e72145c4ae5a..93c016b186c0 100644 > --- a/fs/ext4/super.c > +++ b/fs/ext4/super.c > @@ -735,11 +735,12 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error, > > ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only"); > /* > - * Make sure updated value of ->s_mount_flags will be visible before > - * ->s_flags update > + * EXT4_FLAGS_SHUTDOWN was set which stops all filesystem > + * modifications. We don't set SB_RDONLY because that requires > + * sb->s_umount semaphore and setting it without proper remount > + * procedure is confusing code such as freeze_super() leading to > + * deadlocks and other problems. > */ > - smp_wmb(); > - sb->s_flags |= SB_RDONLY; > } > > static void update_super_work(struct work_struct *work) > -- > 2.35.3 > -- Jan Kara SUSE Labs, CR