Commits
Jie Liu committed 718cc6f88cb
xfs: fix infinite loop by detaching the group/project hints from user dquot xfs_quota(8) will hang up if trying to turn group/project quota off before the user quota is off, this could be 100% reproduced by: # mount -ouquota,gquota /dev/sda7 /xfs # mkdir /xfs/test # xfs_quota -xc 'off -g' /xfs <-- hangs up # echo w > /proc/sysrq-trigger # dmesg SysRq : Show Blocked State task PC stack pid father xfs_quota D 0000000000000000 0 27574 2551 0x00000000 [snip] Call Trace: [<ffffffff81aaa21d>] schedule+0xad/0xc0 [<ffffffff81aa327e>] schedule_timeout+0x35e/0x3c0 [<ffffffff8114b506>] ? mark_held_locks+0x176/0x1c0 [<ffffffff810ad6c0>] ? call_timer_fn+0x2c0/0x2c0 [<ffffffffa0c25380>] ? xfs_qm_shrink_count+0x30/0x30 [xfs] [<ffffffff81aa3306>] schedule_timeout_uninterruptible+0x26/0x30 [<ffffffffa0c26155>] xfs_qm_dquot_walk+0x235/0x260 [xfs] [<ffffffffa0c059d8>] ? xfs_perag_get+0x1d8/0x2d0 [xfs] [<ffffffffa0c05805>] ? xfs_perag_get+0x5/0x2d0 [xfs] [<ffffffffa0b7707e>] ? xfs_inode_ag_iterator+0xae/0xf0 [xfs] [<ffffffffa0c22280>] ? xfs_trans_free_dqinfo+0x50/0x50 [xfs] [<ffffffffa0b7709f>] ? xfs_inode_ag_iterator+0xcf/0xf0 [xfs] [<ffffffffa0c261e6>] xfs_qm_dqpurge_all+0x66/0xb0 [xfs] [<ffffffffa0c2497a>] xfs_qm_scall_quotaoff+0x20a/0x5f0 [xfs] [<ffffffffa0c2b8f6>] xfs_fs_set_xstate+0x136/0x180 [xfs] [<ffffffff8136cf7a>] do_quotactl+0x53a/0x6b0 [<ffffffff812fba4b>] ? iput+0x5b/0x90 [<ffffffff8136d257>] SyS_quotactl+0x167/0x1d0 [<ffffffff814cf2ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f [<ffffffff81abcd19>] system_call_fastpath+0x16/0x1b It's fine if we turn user quota off at first, then turn off other kind of quotas if they are enabled since the group/project dquot refcount is decreased to zero once the user quota if off. Otherwise, those dquots refcount is non-zero due to the user dquot might refer to them as hint(s). Hence, above operation cause an infinite loop at xfs_qm_dquot_walk() while trying to purge dquot cache. This problem has been around since Linux 3.4, it was introduced by: [ b84a3a9675 xfs: remove the per-filesystem list of dquots ] Originally we will release the group dquot pointers because the user dquots maybe carrying around as a hint via xfs_qm_detach_gdquots(). However, with above change, there is no such work to be done before purging group/project dquot cache. In order to solve this problem, this patch introduces a special routine xfs_qm_dqpurge_hints(), and it would release the group/project dquot pointers the user dquots maybe carrying around as a hint, and then it will proceed to purge the user dquot cache if requested. Cc: stable@vger.kernel.org Signed-off-by: Jie Liu <jeff.liu@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Ben Myers <bpm@sgi.com> (cherry picked from commit df8052e7dae00bde6f21b40b6e3e1099770f3afc)