On reboot in 3.14-rt we see this splat: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:905 in_atomic(): 1, irqs_disabled(): 0, pid: 84, name: rcuc/12 Preemption disabled at:[<ffffffff810b29bc>] rcu_cpu_kthread+0x28c/0x700 CPU: 18 PID: 121 Comm: rcuc/18 Tainted: G D 3.14.33-rt28-WR7.0.0.0_ovp+ #2 Hardware name: Intel Corporation S2600CP/S2600CP, BIOS SE5C600.86B.02.01.0002.082220131453 08/22/2013 ffff880fad3e7a70 ffff880fb11cfd58 ffffffff81a0bcee 0000000000000000 ffff880fb11cfd70 ffffffff8107b5eb ffff880fad3e7a40 ffff880fb11cfd88 ffffffff81a136b0 ffff880fad3e7900 ffff880fb11cfdb0 ffffffff811c925c Call Trace: [<ffffffff81a0bcee>] dump_stack+0x4e/0x7a [<ffffffff8107b5eb>] __might_sleep+0xdb/0x150 [<ffffffff81a136b0>] rt_spin_lock+0x20/0x50 [<ffffffff811c925c>] free_ioctx_users+0x2c/0xe0 [<ffffffff8140136b>] percpu_ref_kill_rcu+0x11b/0x120 [<ffffffff810aded5>] rcu_cpu_kthread+0x295/0x6f0 [<ffffffff81076d8d>] smpboot_thread_fn+0x17d/0x2b0 [<ffffffff81a110f0>] ? schedule+0x30/0xa0 [<ffffffff81076c10>] ? SyS_setgroups+0x170/0x170 [<ffffffff8106f4a4>] kthread+0xc4/0xe0 [<ffffffff8106f3e0>] ? flush_kthread_worker+0x90/0x90 [<ffffffff81a147ec>] ret_from_fork+0x7c/0xb0 [<ffffffff8106f3e0>] ? flush_kthread_worker+0x90/0x90 The problem is as stated in lib/percpu-refcount.c: * Note that @release must not sleep - it may potentially be called from RCU * callback context by percpu_ref_kill(). So in -rt the non-raw spinlock trips due to this. The same problem was reported by Mike Galbraith earlier[1] but no conclusive fix was added to the -rt series from that thread. In one post[2], Mike mentions: I was sorely tempted to post a tiny variant that dropped taking ctx_lock in free_ioctx_users() entirely, as someone diddling with no reference didn't make sense. I was thinking the same thing but with a safety net in where we check and warn if anyone else tries to take the lock while we are doing the final garbage collection, which is what we now do here. [1] https://lkml.org/lkml/2014/6/8/10 [2] https://lkml.org/lkml/2014/6/9/979 Cc: Mike Galbraith <umgwanakikbuti@xxxxxxxxx> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx> --- fs/aio.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/aio.c b/fs/aio.c index 2f7e8c2e3e76..d806f7223822 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -539,9 +539,14 @@ static void free_ioctx_users(struct percpu_ref *ref) struct kioctx *ctx = container_of(ref, struct kioctx, users); struct kiocb *req; +#ifndef CONFIG_PREEMPT_RT_BASE spin_lock_irq(&ctx->ctx_lock); +#endif while (!list_empty(&ctx->active_reqs)) { +#ifdef CONFIG_PREEMPT_RT_BASE + WARN_ON(spin_is_locked(&ctx->ctx_lock)); +#endif req = list_first_entry(&ctx->active_reqs, struct kiocb, ki_list); @@ -549,7 +554,9 @@ static void free_ioctx_users(struct percpu_ref *ref) kiocb_cancel(ctx, req); } +#ifndef CONFIG_PREEMPT_RT_BASE spin_unlock_irq(&ctx->ctx_lock); +#endif percpu_ref_kill(&ctx->reqs); percpu_ref_put(&ctx->reqs); -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
