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| /openbmc/linux/fs/quota/ |
| H A D | dquot.c | d01730d7 Tue Jul 07 11:15:21 CDT 2009 Jiaying Zhang <jiayingz@google.com> quota: Fix possible deadlock during parallel quotaon and quotaoff
The following test script triggers a deadlock on ext2 filesystem:
while true; do quotaon /dev/hda >&/dev/null; usleep $RANDOM; done &
while true; do quotaoff /dev/hda >&/dev/null; usleep $RANDOM; done &
I found there is a potential deadlock between quotaon and quotaoff (or
quotasync). Basically, all of quotactl operations need to be protected by
dqonoff_mutex. vfs_quota_off and vfs_quota_sync also call sb->s_op->quota_write
that needs to grab the i_mutex of the quota file. But in vfs_quota_on_inode
(called from quotaon operation), the current code tries to grab the i_mutex of
the quota file first before getting quonoff_mutex.
Reverse the order in which we take locks in vfs_quota_on_inode().
Jan Kara: Changed changelog to be more readable, made lockdep happy with
I_MUTEX_QUOTA.
Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
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