On 12/18/14 00:06, Mike Snitzer wrote:
> So if you know someone with relevant blk-mq hardware who might benefit
> from blk-mq multipathing please point them at this code and have them
> report back!
Hello Mike,
Great to see that you are working on blk-mq multipathing. Unfortunately
a test with the SRP initiator and your dm-for-3.20-blk-mq tree merged
with Linus' latest tree was not successful. This is what was reported
when I tried to start multipathd (without call trace, followed by a
hard lockup):
=========================================================
[ INFO: possible irq lock inversion dependency detected ]
3.18.0-debug+ #1 Tainted: G W
---------------------------------------------------------
kdmwork-253:0/5347 just changed the state of lock:
(&(&m->lock)->rlock){+.....}, at: [<ffffffffa080eb80>] __multipath_map.isra.15+0x40/0x1f0 [dm_multipath]
but this lock was taken by another, HARDIRQ-safe lock in the past:
(&(&q->__queue_lock)->rlock){-.-...}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
This is how objdump translates the assembler code of the above kernel address (0x1b80 below):
static int __multipath_map(struct dm_target *ti, struct request *clone,
1b62: 48 89 55 c8 mov %rdx,-0x38(%rbp)
1b66: 4c 89 45 c0 mov %r8,-0x40(%rbp)
union map_info *map_context,
struct request *rq, struct request **__clone)
{
struct multipath *m = (struct multipath *) ti->private;
int r = DM_MAPIO_REQUEUE;
size_t nr_bytes = clone ? blk_rq_bytes(clone) : blk_rq_bytes(rq);
1b6a: 0f 84 50 01 00 00 je 1cc0 <__multipath_map.isra.15+0x180>
1b70: 44 8b 66 5c mov 0x5c(%rsi),%r12d
raw_spin_lock_init(&(_lock)->rlock); \
} while (0)
static inline void spin_lock(spinlock_t *lock)
{
raw_spin_lock(&lock->rlock);
1b74: 49 8d 5e 28 lea 0x28(%r14),%rbx
1b78: 48 89 df mov %rbx,%rdi
1b7b: e8 00 00 00 00 callq 1b80 <__multipath_map.isra.15+0x40>
struct dm_mpath_io *mpio;
spin_lock(&m->lock);
/* Do we need to select a new pgpath? */
if (!m->current_pgpath ||
1b80: 49 8b 8e d0 00 00 00 mov 0xd0(%r14),%rcx
1b87: 48 85 c9 test %rcx,%rcx
1b8a: 74 55 je 1be1 <__multipath_map.isra.15+0xa1>
(!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
1b8c: 41 0f b6 96 ec 00 00 movzbl 0xec(%r14),%edx
Bart.
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