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authorTomoki Sekiyama <tomoki.sekiyama@hds.com>2013-10-15 16:42:16 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-12-08 07:29:27 -0800
commit6d53d39270ccd29938dcbd611a44870c63032521 (patch)
tree37b7167ad0620ec2dbddd469acc44f97bc5332fa /block
parent645451235dc5098f08cc51e2f1205d9fa9ca8262 (diff)
downloadlinaro-lsk-6d53d39270ccd29938dcbd611a44870c63032521.tar.gz
elevator: Fix a race in elevator switching and md device initialization
commit eb1c160b22655fd4ec44be732d6594fd1b1e44f4 upstream. The soft lockup below happens at the boot time of the system using dm multipath and the udev rules to switch scheduler. [ 356.127001] BUG: soft lockup - CPU#3 stuck for 22s! [sh:483] [ 356.127001] RIP: 0010:[<ffffffff81072a7d>] [<ffffffff81072a7d>] lock_timer_base.isra.35+0x1d/0x50 ... [ 356.127001] Call Trace: [ 356.127001] [<ffffffff81073810>] try_to_del_timer_sync+0x20/0x70 [ 356.127001] [<ffffffff8118b08a>] ? kmem_cache_alloc_node_trace+0x20a/0x230 [ 356.127001] [<ffffffff810738b2>] del_timer_sync+0x52/0x60 [ 356.127001] [<ffffffff812ece22>] cfq_exit_queue+0x32/0xf0 [ 356.127001] [<ffffffff812c98df>] elevator_exit+0x2f/0x50 [ 356.127001] [<ffffffff812c9f21>] elevator_change+0xf1/0x1c0 [ 356.127001] [<ffffffff812caa50>] elv_iosched_store+0x20/0x50 [ 356.127001] [<ffffffff812d1d09>] queue_attr_store+0x59/0xb0 [ 356.127001] [<ffffffff812143f6>] sysfs_write_file+0xc6/0x140 [ 356.127001] [<ffffffff811a326d>] vfs_write+0xbd/0x1e0 [ 356.127001] [<ffffffff811a3ca9>] SyS_write+0x49/0xa0 [ 356.127001] [<ffffffff8164e899>] system_call_fastpath+0x16/0x1b This is caused by a race between md device initialization by multipathd and shell script to switch the scheduler using sysfs. - multipathd: SyS_ioctl -> do_vfs_ioctl -> dm_ctl_ioctl -> ctl_ioctl -> table_load -> dm_setup_md_queue -> blk_init_allocated_queue -> elevator_init q->elevator = elevator_alloc(q, e); // not yet initialized - sh -c 'echo deadline > /sys/$DEVPATH/queue/scheduler': elevator_switch (in the call trace above) struct elevator_queue *old = q->elevator; q->elevator = elevator_alloc(q, new_e); elevator_exit(old); // lockup! (*) - multipathd: (cont.) err = e->ops.elevator_init_fn(q); // init fails; q->elevator is modified (*) When del_timer_sync() is called, lock_timer_base() will loop infinitely while timer->base == NULL. In this case, as timer will never initialized, it results in lockup. This patch introduces acquisition of q->sysfs_lock around elevator_init() into blk_init_allocated_queue(), to provide mutual exclusion between initialization of the q->scheduler and switching of the scheduler. This should fix this bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=902012 Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'block')
-rw-r--r--block/blk-core.c10
-rw-r--r--block/elevator.c6
2 files changed, 15 insertions, 1 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index acf3bf6a44d..2c66daba44d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -741,9 +741,17 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
q->sg_reserved_size = INT_MAX;
+ /* Protect q->elevator from elevator_change */
+ mutex_lock(&q->sysfs_lock);
+
/* init elevator */
- if (elevator_init(q, NULL))
+ if (elevator_init(q, NULL)) {
+ mutex_unlock(&q->sysfs_lock);
return NULL;
+ }
+
+ mutex_unlock(&q->sysfs_lock);
+
return q;
}
EXPORT_SYMBOL(blk_init_allocated_queue);
diff --git a/block/elevator.c b/block/elevator.c
index 668394d1858..02d4390afee 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -186,6 +186,12 @@ int elevator_init(struct request_queue *q, char *name)
struct elevator_type *e = NULL;
int err;
+ /*
+ * q->sysfs_lock must be held to provide mutual exclusion between
+ * elevator_switch() and here.
+ */
+ lockdep_assert_held(&q->sysfs_lock);
+
if (unlikely(q->elevator))
return 0;