On 2013/11/26 22:03, Peter Zijlstra wrote: > Juri hit the below lockdep report: > > [ 4.303391] ====================================================== > [ 4.303392] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ] > [ 4.303394] 3.12.0-dl-peterz+ #144 Not tainted > [ 4.303395] ------------------------------------------------------ > [ 4.303397] kworker/u4:3/689 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: > [ 4.303399] (&p->mems_allowed_seq){+.+...}, at: [<ffffffff8114e63c>] new_slab+0x6c/0x290 > [ 4.303417] > [ 4.303417] and this task is already holding: > [ 4.303418] (&(&q->__queue_lock)->rlock){..-...}, at: [<ffffffff812d2dfb>] blk_execute_rq_nowait+0x5b/0x100 > [ 4.303431] which would create a new lock dependency: > [ 4.303432] (&(&q->__queue_lock)->rlock){..-...} -> (&p->mems_allowed_seq){+.+...} > [ 4.303436] > > [ 4.303898] the dependencies between the lock to be acquired and SOFTIRQ-irq-unsafe lock: > [ 4.303918] -> (&p->mems_allowed_seq){+.+...} ops: 2762 { > [ 4.303922] HARDIRQ-ON-W at: > [ 4.303923] [<ffffffff8108ab9a>] __lock_acquire+0x65a/0x1ff0 > [ 4.303926] [<ffffffff8108cbe3>] lock_acquire+0x93/0x140 > [ 4.303929] [<ffffffff81063dd6>] kthreadd+0x86/0x180 > [ 4.303931] [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0 > [ 4.303933] SOFTIRQ-ON-W at: > [ 4.303933] [<ffffffff8108abcc>] __lock_acquire+0x68c/0x1ff0 > [ 4.303935] [<ffffffff8108cbe3>] lock_acquire+0x93/0x140 > [ 4.303940] [<ffffffff81063dd6>] kthreadd+0x86/0x180 > [ 4.303955] [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0 > [ 4.303959] INITIAL USE at: > [ 4.303960] [<ffffffff8108a884>] __lock_acquire+0x344/0x1ff0 > [ 4.303963] [<ffffffff8108cbe3>] lock_acquire+0x93/0x140 > [ 4.303966] [<ffffffff81063dd6>] kthreadd+0x86/0x180 > [ 4.303969] [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0 > [ 4.303972] } > > Which reports that we take mems_allowed_seq with interrupts enabled. A > little digging found that this can only be from > cpuset_change_task_nodemask(). > Yeah, the other one in set_mems_allowed() was fixed by John. > This is an actual deadlock because an interrupt doing an allocation will > hit get_mems_allowed()->...->__read_seqcount_begin(), which will spin > forever waiting for the write side to complete. > > Cc: John Stultz <john.stultz@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Reported-by: Juri Lelli <juri.lelli@xxxxxxxxx> > Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Acked-by: Li Zefan <lizefan@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>