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Fix kernel panic due to tsd_exit in ZFS_EXIT(zsb)
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The following panic would occur under certain heavy load:
[ 4692.202686] Kernel panic - not syncing: thread ffff8800c4f5dd60 terminating with rrw lock ffff8800da1b9c40 held
[ 4692.228053] CPU: 1 PID: 6250 Comm: mmap_deadlock Tainted: P           OE  3.18.10 #7

The culprit is that ZFS_EXIT(zsb) would call tsd_exit() every time, which
would purge all tsd data for the thread. However, ZFS_ENTER is designed to be
reentrant, so we cannot allow ZFS_EXIT to blindly purge tsd data.

Instead, we rely on the new behavior of tsd_set. When NULL is passed as the
new value to tsd_set, it will automatically remove the tsd entry specified the
the key for the current thread.

rrw_tsd_key and zfs_allow_log_key already calls tsd_set(key, NULL) when
they're done. The zfs_fsyncer_key relied on ZFS_EXIT(zsb) to call tsd_exit() to
do clean up. Now we explicitly call tsd_set(key, NULL) on them.

Signed-off-by: Chunwei Chen <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#3247
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tuxoko authored and behlendorf committed Apr 24, 2015
1 parent 59199d9 commit 07012da
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Showing 2 changed files with 2 additions and 1 deletion.
1 change: 0 additions & 1 deletion include/sys/zfs_znode.h
Original file line number Diff line number Diff line change
Expand Up @@ -263,7 +263,6 @@ typedef struct znode {
#define ZFS_EXIT(zsb) \
{ \
rrw_exit(&(zsb)->z_teardown_lock, FTAG); \
tsd_exit(); \
}

/* Verifies the znode is valid */
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2 changes: 2 additions & 0 deletions module/zfs/zfs_vnops.c
Original file line number Diff line number Diff line change
Expand Up @@ -2156,6 +2156,8 @@ zfs_fsync(struct inode *ip, int syncflag, cred_t *cr)
zil_commit(zsb->z_log, zp->z_id);
ZFS_EXIT(zsb);
}
tsd_set(zfs_fsyncer_key, NULL);

return (0);
}
EXPORT_SYMBOL(zfs_fsync);
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