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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org,
	harshad shirwadkar <harshadshirwadkar@gmail.com>,
	stable@vger.kernel.org, Tahsin Erdogan <tahsin@google.com>
Subject: Re: [PATCH 6/8] ext4: Fix deadlock with fs freezing and EA inodes
Date: Thu, 17 Dec 2020 11:01:25 -0500	[thread overview]
Message-ID: <X9uA1Wo0tD8sUgAB@mit.edu> (raw)
In-Reply-To: <20201216101844.22917-7-jack@suse.cz>

On Wed, Dec 16, 2020 at 11:18:42AM +0100, Jan Kara wrote:
> Xattr code using inodes with large xattr data can end up dropping last
> inode reference (and thus deleting the inode) from places like
> ext4_xattr_set_entry(). That function is called with transaction started
> and so ext4_evict_inode() can deadlock against fs freezing like:
> 
> CPU1					CPU2
> 
> removexattr()				freeze_super()
>   vfs_removexattr()
>     ext4_xattr_set()
>       handle = ext4_journal_start()
>       ...
>       ext4_xattr_set_entry()
>         iput(old_ea_inode)
>           ext4_evict_inode(old_ea_inode)
> 					  sb->s_writers.frozen = SB_FREEZE_FS;
> 					  sb_wait_write(sb, SB_FREEZE_FS);
> 					  ext4_freeze()
> 					    jbd2_journal_lock_updates()
> 					      -> blocks waiting for all
> 					         handles to stop
>             sb_start_intwrite()
> 	      -> blocks as sb is already in SB_FREEZE_FS state
> 
> Generally it is advisable to delete inodes from a separate transaction
> as it can consume quite some credits however in this case it would be
> quite clumsy and furthermore the credits for inode deletion are quite
> limited and already accounted for. So just tweak ext4_evict_inode() to
> avoid freeze protection if we have transaction already started and thus
> it is not really needed anyway.
> 
> CC: stable@vger.kernel.org
> Fixes: dec214d00e0d ("ext4: xattr inode deduplication")
> CC: Tahsin Erdogan <tahsin@google.com>
> Signed-off-by: Jan Kara <jack@suse.cz>

Already applied.

						- Ted

  reply	other threads:[~2020-12-17 16:02 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-16 10:18 [PATCH 0/8 v2 PARTIAL] ext4: Fix error handling Jan Kara
2020-12-16 10:18 ` [PATCH 1/8] ext4: Combine ext4_handle_error() and save_error_info() Jan Kara
2020-12-17 15:50   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 2/8] ext4: Drop sync argument of ext4_commit_super() Jan Kara
2020-12-17 15:51   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 3/8] ext4: Protect superblock modifications with a buffer lock Jan Kara
2020-12-17 15:56   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 4/8] ext4: Save error info to sb through journal if available Jan Kara
2020-12-17 15:58   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 5/8] ext4: Use sbi instead of EXT4_SB(sb) in ext4_update_super() Jan Kara
2020-12-17 15:59   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 6/8] ext4: Fix deadlock with fs freezing and EA inodes Jan Kara
2020-12-17 16:01   ` Theodore Y. Ts'o [this message]
2020-12-16 10:18 ` [PATCH 7/8] ext4: Fix superblock checksum failure when setting password salt Jan Kara
2020-12-17 16:02   ` Theodore Y. Ts'o
2020-12-16 10:18 ` [PATCH 8/8] ext4: Drop ext4_handle_dirty_super() Jan Kara
2020-12-17 16:08   ` Theodore Y. Ts'o

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