From: Jiaying Zhang Date: Tue, 7 Jul 2009 16:15:21 +0000 (+0200) Subject: quota: Fix possible deadlock during parallel quotaon and quotaoff X-Git-Tag: v2.6.31-rc3~51^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d01730d74d2b0155da50d44555001706294014f7;p=pandora-kernel.git 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 Signed-off-by: Jan Kara --- Reading git-diff-tree failed