* Gu Zheng <guz.f...@cn.fujitsu.com> wrote:
> The following lockdep warning occurrs when running with latest kernel:
> [ 3.178000] ------------[ cut here ]------------
> [ 3.183000] WARNING: CPU: 128 PID: 0 at kernel/locking/lockdep.c:2755
> lockdep_trace_alloc+0xdd/0xe0()
> [ 3.193000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> [ 3.199000] Modules linked in:
>
> [ 3.203000] CPU: 128 PID: 0 Comm: swapper/128 Not tainted 4.1.0-rc3 #70
> [ 3.221000] 0000000000000000 2d6601fb3e6d4e4c ffff88086fd5fc38
> ffffffff81773f0a
> [ 3.230000] 0000000000000000 ffff88086fd5fc90 ffff88086fd5fc78
> ffffffff8108c85a
> [ 3.238000] ffff88086fd60000 0000000000000092 ffff88086fd60000
> 00000000000000d0
> [ 3.246000] Call Trace:
> [ 3.249000] [<ffffffff81773f0a>] dump_stack+0x4c/0x65
> [ 3.255000] [<ffffffff8108c85a>] warn_slowpath_common+0x8a/0xc0
> [ 3.261000] [<ffffffff8108c8e5>] warn_slowpath_fmt+0x55/0x70
> [ 3.268000] [<ffffffff810ee24d>] lockdep_trace_alloc+0xdd/0xe0
> [ 3.274000] [<ffffffff811cda0d>] __alloc_pages_nodemask+0xad/0xca0
> [ 3.281000] [<ffffffff810ec7ad>] ? __lock_acquire+0xf6d/0x1560
> [ 3.288000] [<ffffffff81219c8a>] alloc_page_interleave+0x3a/0x90
> [ 3.295000] [<ffffffff8121b32d>] alloc_pages_current+0x17d/0x1a0
> [ 3.301000] [<ffffffff811c869e>] ? __get_free_pages+0xe/0x50
> [ 3.308000] [<ffffffff811c869e>] __get_free_pages+0xe/0x50
> [ 3.314000] [<ffffffff8102640b>] init_espfix_ap+0x17b/0x320
> [ 3.320000] [<ffffffff8105c691>] start_secondary+0xf1/0x1f0
> [ 3.327000] ---[ end trace 1b3327d9d6a1d62c ]---
>
> This seems a mis-warning by lockdep, as we alloc pages with GFP_KERNEL in
> init_espfix_ap() which is called before enabled local irq, and the lockdep
> sub-system considers this behaviour as allocating memory with GFP_FS with
> local
> irq disabled, then trigger the warning as mentioned about.
Why should this be a 'mis-warning'? If the GFP_KERNEL allocation sleeps then
we'll
sleep with irqs disabled => bad.
This looks like a real (albeit hard to trigger) bug.
> Though we could allocate them on the boot CPU side and hand them over to the
> secondary CPU, but it seemes a bit waste if some of cpus are offline. As
> thers
> is no need to these pages(espfix stack) until we try to run user code, so we
> postpone the initialization of espfix stack after cpu booted to avoid the
> noise.
> -void init_espfix_ap(void)
> +void init_espfix_ap(int cpu)
> {
So how about the concern I raised in a former thread, that the allocation
should
be done for the node the target CPU is on? The 'cpu' parameter should be
propagated to the allocation as well, and turned into a node allocation or so.
Even though some CPUs will share the espfix stack, some won't.
Thanks,
Ingo
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