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From: Luis Henriques To: Jan Kara Cc: "Luis Henriques (SUSE)" , Theodore Ts'o , Andreas Dilger , Harshad Shirwadkar , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] ext4: fix fast commit inode enqueueing during a full journal commit In-Reply-To: <20240524162231.l5r4niz7awjgfju6@quack3> (Jan Kara's message of "Fri, 24 May 2024 18:22:31 +0200") References: <20240523111618.17012-1-luis.henriques@linux.dev> <20240524162231.l5r4niz7awjgfju6@quack3> Date: Mon, 27 May 2024 09:29:40 +0100 Message-ID: <87h6ej64jv.fsf@brahms.olymp> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT On Fri 24 May 2024 06:22:31 PM +02, Jan Kara wrote; > On Thu 23-05-24 12:16:18, Luis Henriques (SUSE) wrote: >> When a full journal commit is on-going, any fast commit has to be enqueu= ed >> into a different queue: FC_Q_STAGING instead of FC_Q_MAIN. This enqueue= ing >> is done only once, i.e. if an inode is already queued in a previous fast >> commit entry it won't be enqueued again. However, if a full commit star= ts >> _after_ the inode is enqueued into FC_Q_MAIN, the next fast commit needs= to >> be done into FC_Q_STAGING. And this is not being done in function >> ext4_fc_track_template(). >>=20 >> This patch fixes the issue by flagging an inode that is already enqueued= in >> either queues. Later, during the fast commit clean-up callback, if the >> inode has a tid that is bigger than the one being handled, that inode is >> re-enqueued into STAGING and the spliced back into MAIN. >>=20 >> This bug was found using fstest generic/047. This test creates several = 32k >> bytes files, sync'ing each of them after it's creation, and then shutting >> down the filesystem. Some data may be loss in this operation; for examp= le a >> file may have it's size truncated to zero. >>=20 >> Signed-off-by: Luis Henriques (SUSE) > > Thanks for the fix. Some comments below: > >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h >> index 983dad8c07ec..4c308c18c3da 100644 >> --- a/fs/ext4/ext4.h >> +++ b/fs/ext4/ext4.h >> @@ -1062,9 +1062,18 @@ struct ext4_inode_info { >> /* Fast commit wait queue for this inode */ >> wait_queue_head_t i_fc_wait; >>=20=20 >> - /* Protect concurrent accesses on i_fc_lblk_start, i_fc_lblk_len */ >> + /* >> + * Protect concurrent accesses on i_fc_lblk_start, i_fc_lblk_len, >> + * i_fc_next >> + */ >> struct mutex i_fc_lock; >>=20=20 >> + /* >> + * Used to flag an inode as part of the next fast commit; will be >> + * reset during fast commit clean-up >> + */ >> + tid_t i_fc_next; >> + > > Do we really need new tid in the inode? I'd be kind of hoping we could use > EXT4_I(inode)->i_sync_tid for this - I can see we even already set it in > ext4_fc_track_template() and used for similar comparisons in fast commit > code. Ah, true. It looks like it could be used indeed. We'll still need a flag here, but a simple bool should be enough for that. > >> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c >> index 87c009e0c59a..bfdf249f0783 100644 >> --- a/fs/ext4/fast_commit.c >> +++ b/fs/ext4/fast_commit.c >> @@ -402,6 +402,8 @@ static int ext4_fc_track_template( >> sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) ? >> &sbi->s_fc_q[FC_Q_STAGING] : >> &sbi->s_fc_q[FC_Q_MAIN]); >> + else >> + ei->i_fc_next =3D tid; >> spin_unlock(&sbi->s_fc_lock); >>=20=20 >> return ret; >> @@ -1280,6 +1282,15 @@ static void ext4_fc_cleanup(journal_t *journal, i= nt full, tid_t tid) >> list_for_each_entry_safe(iter, iter_n, &sbi->s_fc_q[FC_Q_MAIN], >> i_fc_list) { >> list_del_init(&iter->i_fc_list); >> + if (iter->i_fc_next =3D=3D tid) >> + iter->i_fc_next =3D 0; >> + else if (iter->i_fc_next > tid) > ^^^ careful here, TIDs do wrap so you need to use > tid_geq() for comparison. > Yikes! Thanks, I'll update the code to do that. >> + /* >> + * re-enqueue inode into STAGING, which will later be >> + * splice back into MAIN >> + */ >> + list_add_tail(&EXT4_I(&iter->vfs_inode)->i_fc_list, >> + &sbi->s_fc_q[FC_Q_STAGING]); >> ext4_clear_inode_state(&iter->vfs_inode, >> EXT4_STATE_FC_COMMITTING); >> if (iter->i_sync_tid <=3D tid) > ^^^ and I can see this is buggy as > well and needs tid_geq() (not your fault obviously). Yeah, good point. I can that too in v3. Again, thanks a lot for your review! Cheers, --=20 Lu=C3=ADs