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