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From: Jan Kara <jack@suse.cz>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Jan Kara <jack@suse.cz>, linux-ext4@vger.kernel.org
Subject: Re: [PATCH 08/22] ext4: Provide function to handle transaction restarts
Date: Wed, 23 Oct 2019 18:25:13 +0200	[thread overview]
Message-ID: <20191023162513.GF31271@quack2.suse.cz> (raw)
In-Reply-To: <20191021162046.GA27850@mit.edu>

On Mon 21-10-19 12:20:46, Theodore Y. Ts'o wrote:
> On Fri, Oct 04, 2019 at 12:05:54AM +0200, Jan Kara wrote:
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index fb0f99dc8c22..32f2c22c7ef2 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> 
> > +/*
> > + * Make sure 'handle' has at least 'check_cred' credits. If not, restart
> > + * transaction with 'restart_cred' credits. The function drops i_data_sem
> > + * when restarting transaction and gets it after transaction is restarted.
> > + *
> > + * The function returns 0 on success, 1 if transaction had to be restarted,
> > + * and < 0 in case of fatal error.
> > + */
> > +int ext4_datasem_ensure_credits(handle_t *handle, struct inode *inode,
> > +				int check_cred, int restart_cred)
> 
> This makes me super nervous.  This gets called by ext4_access_path(),
> which in turn is called by the insert_range, and collapse_range (among
> others) where we previously were not dropping i_data_sem.  This means
> we will be dropping i_data_sem while they are in the middle of doing
> surgery to the extent tree, which makes me super nervous.

But this patch changes nothing in that regard. Previously,
ext4_access_path() was using ext4_ext_truncate_extend_restart() which
called ext4_truncate_restart_trans() which was dropping i_data_sem as well.

> Granted, insert_range and collapse_range take a lot of locks,
> including the inode lock, but it's not obvious to me that this is
> safe, and at the very least the documentation for ext4_access_path
> should have a warning note in its comments that i_data_sem can get
> dropped, and its call sites audited if they haven't already.

Yeah, comment about that would be nice. I can add that when touching this
function anyway.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2019-10-23 16:25 UTC|newest]

Thread overview: 101+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 22:05 [PATCH 0/19 v3] ext4: Fix transaction overflow due to revoke descriptors Jan Kara
2019-10-03 22:05 ` [PATCH 01/22] jbd2: Fix possible overflow in jbd2_log_space_left() Jan Kara
2019-10-21  1:08   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 02/22] jbd2: Fixup stale comment in commit code Jan Kara
2019-10-21  1:08   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 03/22] ext4: Do not iput inode under running transaction in ext4_mkdir() Jan Kara
2019-10-21  1:21   ` Theodore Y. Ts'o
2019-10-24 10:19     ` Jan Kara
2019-10-24 12:09       ` Theodore Y. Ts'o
2019-10-24 13:37         ` Jan Kara
2019-11-04 12:35           ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 04/22] ext4: Fix credit estimate for final inode freeing Jan Kara
2019-10-21  1:07   ` Theodore Y. Ts'o
2019-10-24 10:30     ` Jan Kara
2019-10-03 22:05 ` [PATCH 05/22] ext4: Fix ext4_should_journal_data() for EA inodes Jan Kara
2019-10-21  1:38   ` Theodore Y. Ts'o
2019-10-23 16:55     ` Jan Kara
2019-10-03 22:05 ` [PATCH 06/22] ext4: Use ext4_journal_extend() instead of jbd2_journal_extend() Jan Kara
2019-10-21  1:39   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 07/22] ext4: Avoid unnecessary revokes in ext4_alloc_branch() Jan Kara
2019-10-21 13:39   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 08/22] ext4: Provide function to handle transaction restarts Jan Kara
2019-10-21 16:20   ` Theodore Y. Ts'o
2019-10-23 16:25     ` Jan Kara [this message]
2019-10-03 22:05 ` [PATCH 09/22] ext4, jbd2: Provide accessor function for handle credits Jan Kara
2019-10-21 16:21   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 10/22] ocfs2: Use accessor function for h_buffer_credits Jan Kara
2019-10-21 16:21   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 11/22] jbd2: Fix statistics for the number of logged blocks Jan Kara
2019-10-21 16:24   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 12/22] jbd2: Reorganize jbd2_journal_stop() Jan Kara
2019-10-21 17:29   ` Theodore Y. Ts'o
2019-10-03 22:05 ` [PATCH 13/22] jbd2: Drop pointless check from jbd2_journal_stop() Jan Kara
2019-10-21 17:30   ` Theodore Y. Ts'o
2019-10-03 22:06 ` [PATCH 14/22] jbd2: Drop pointless wakeup " Jan Kara
2019-10-21 17:34   ` Theodore Y. Ts'o
2019-10-03 22:06 ` [PATCH 15/22] jbd2: Factor out common parts of stopping and restarting a handle Jan Kara
2019-10-21 17:49   ` Theodore Y. Ts'o
2019-10-23 16:17     ` Jan Kara
2019-11-04 12:36       ` Theodore Y. Ts'o
2019-11-04 12:59         ` Jan Kara
2019-10-03 22:06 ` [PATCH 16/22] jbd2: Account descriptor blocks into t_outstanding_credits Jan Kara
2019-10-21 21:04   ` Theodore Y. Ts'o
2019-10-23 13:09     ` Jan Kara
2019-10-03 22:06 ` [PATCH 17/22] jbd2: Drop jbd2_space_needed() Jan Kara
2019-10-21 21:05   ` Theodore Y. Ts'o
2019-10-03 22:06 ` [PATCH 18/22] jbd2: Reserve space for revoke descriptor blocks Jan Kara
2019-10-21 21:47   ` Theodore Y. Ts'o
2019-10-23 13:27     ` Jan Kara
2019-10-03 22:06 ` [PATCH 19/22] jbd2: Rename h_buffer_credits to h_total_credits Jan Kara
2019-10-21 21:48   ` Theodore Y. Ts'o
2019-10-03 22:06 ` [PATCH 20/22] jbd2: Make credit checking more strict Jan Kara
2019-10-21 22:29   ` Theodore Y. Ts'o
2019-10-23 13:30     ` Jan Kara
2019-10-03 22:06 ` [PATCH 21/22] ext4: Reserve revoke credits for freed blocks Jan Kara
2019-10-21 23:18   ` Theodore Y. Ts'o
2019-10-23 16:13     ` Jan Kara
2019-11-04 13:08       ` Theodore Y. Ts'o
2019-11-05  8:31         ` Jan Kara
2019-10-03 22:06 ` [PATCH 22/22] jbd2: Provide trace event for handle restarts Jan Kara
2019-10-21 23:18   ` Theodore Y. Ts'o
2019-10-19 19:19 ` [PATCH 0/19 v3] ext4: Fix transaction overflow due to revoke descriptors Theodore Y. Ts'o
2019-10-24 13:09   ` Jan Kara
2019-10-24 15:12     ` Jan Kara
2019-11-04  3:32 ` Theodore Y. Ts'o
2019-11-04 11:22   ` Jan Kara
2019-11-04 13:09     ` Theodore Y. Ts'o
2019-11-05 16:44 ` [PATCH 0/25 " Jan Kara
2019-11-05 16:44 ` [PATCH 01/25] jbd2: Fix possible overflow in jbd2_log_space_left() Jan Kara
2019-11-05 16:44 ` [PATCH 02/25] jbd2: Fixup stale comment in commit code Jan Kara
2019-11-05 16:44 ` [PATCH 03/25] jbd2: Completely fill journal descriptor blocks Jan Kara
2019-11-05 16:44 ` [PATCH 04/25] ext4: Move marking of handle as sync to ext4_add_nondir() Jan Kara
2019-11-05 16:44 ` [PATCH 05/25] ext4: Do not iput inode under running transaction Jan Kara
2019-11-05 16:44 ` [PATCH 06/25] ext4: Fix credit estimate for final inode freeing Jan Kara
2019-11-05 21:00   ` Theodore Y. Ts'o
2019-11-05 16:44 ` [PATCH 07/25] ext4: Fix ext4_should_journal_data() for EA inodes Jan Kara
2019-11-05 16:44 ` [PATCH 08/25] ext4: Use ext4_journal_extend() instead of jbd2_journal_extend() Jan Kara
2019-11-05 16:44 ` [PATCH 09/25] ext4: Avoid unnecessary revokes in ext4_alloc_branch() Jan Kara
2019-11-05 16:44 ` [PATCH 10/25] ext4: Provide function to handle transaction restarts Jan Kara
2019-11-05 16:44 ` [PATCH 11/25] ext4, jbd2: Provide accessor function for handle credits Jan Kara
2019-11-05 16:44 ` [PATCH 12/25] ocfs2: Use accessor function for h_buffer_credits Jan Kara
2019-11-05 16:44 ` [PATCH 13/25] jbd2: Fix statistics for the number of logged blocks Jan Kara
2019-11-05 16:44 ` [PATCH 14/25] jbd2: Reorganize jbd2_journal_stop() Jan Kara
2019-11-05 16:44 ` [PATCH 15/25] jbd2: Drop pointless check from jbd2_journal_stop() Jan Kara
2019-11-05 16:44 ` [PATCH 16/25] jbd2: Drop pointless wakeup " Jan Kara
2019-11-05 16:44 ` [PATCH 17/25] jbd2: Factor out common parts of stopping and restarting a handle Jan Kara
2019-11-05 16:44 ` [PATCH 18/25] jbd2: Account descriptor blocks into t_outstanding_credits Jan Kara
2019-11-05 16:44 ` [PATCH 19/25] jbd2: Drop jbd2_space_needed() Jan Kara
2019-11-05 16:44 ` [PATCH 20/25] jbd2: Reserve space for revoke descriptor blocks Jan Kara
2019-11-15  7:52   ` Eric Biggers
2019-11-15 10:02     ` Jan Kara
2019-11-15 14:20       ` Theodore Y. Ts'o
2019-11-15 17:10         ` Eric Biggers
2019-11-05 16:44 ` [PATCH 21/25] jbd2: Rename h_buffer_credits to h_total_credits Jan Kara
2019-11-05 16:44 ` [PATCH 22/25] jbd2: Make credit checking more strict Jan Kara
2019-11-05 16:44 ` [PATCH 23/25] ext4: Reserve revoke credits for freed blocks Jan Kara
2019-11-05 16:44 ` [PATCH 24/25] jbd2: Provide trace event for handle restarts Jan Kara
2019-11-05 16:44 ` [PATCH 25/25] jbd2: Fine tune estimate of necessary descriptor blocks Jan Kara
2019-11-05 21:04 ` [PATCH 0/25 v3] ext4: Fix transaction overflow due to revoke descriptors Theodore Y. Ts'o
     [not found] ` <20191112220614.GA11089@mit.edu>
     [not found]   ` <20191113094545.GC6367@quack2.suse.cz>
2019-11-14  5:26     ` [PATCH 0/19 " Theodore Y. Ts'o
2019-11-14  8:49       ` Jan Kara

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