Messages in this thread | | | From | Tomoki Sekiyama <> | Subject | Re: [PATCH v2 1/2] elevator: Fix a race in elevator switching and md device initialization | Date | Fri, 6 Sep 2013 15:01:08 +0000 |
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Ping: any comments for this series?
On 8/30/13 18:47 , "Tomoki Sekiyama" <tomoki.sekiyama@hds.com> wrote:
>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> >--- > block/blk-core.c | 10 +++++++++- > block/elevator.c | 6 ++++++ > 2 files changed, 15 insertions(+), 1 deletion(-) > >diff --git a/block/blk-core.c b/block/blk-core.c >index 93a18d1..2f6275f 100644 >--- a/block/blk-core.c >+++ b/block/blk-core.c >@@ -739,9 +739,17 @@ 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 668394d..02d4390 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; > >
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