Re: [RFC PATCH] x86, espfix: use spin_lock rather than mutex
From: Ingo Molnar
Date: Thu May 14 2015 - 14:30:08 EST
* Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Thu, May 14, 2015 at 07:37:45PM +0800, Gu Zheng 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.
> > Though here we use GFP_NOFS rather GFP_KERNEL to avoid the warning, but
> > you know, init_espfix_ap is called with preempt and local irq disabled,
> > it is not a good idea to use mutex (might sleep) here.
> > So we convert the initialization lock to spin_lock here to avoid the noise.
> >
> > Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
> > Cc: Stable <stable@xxxxxxxxxxxxxxx>
> > ---
> > arch/x86/kernel/espfix_64.c | 13 +++++++------
> > 1 files changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
> > index f5d0730..ceb35a3 100644
> > --- a/arch/x86/kernel/espfix_64.c
> > +++ b/arch/x86/kernel/espfix_64.c
> > @@ -57,14 +57,14 @@
> > # error "Need more than one PGD for the ESPFIX hack"
> > #endif
> >
> > -#define PGALLOC_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO)
> > +#define PGALLOC_GFP (GFP_ATOMIC | __GFP_NOTRACK | __GFP_ZERO)
>
> IINM, that's ESPFIX_MAX_PAGES with GFP_ATOMIC which for 8K CPUs are 128
> pages.
>
> That's a lotta waste in my book for espfix stack pages.
>
> Enabling interrupts earlier in start_secondary() is probably out of
> the question, maybe we should prealloc all those pages...
We could allocate them on the boot CPU side and hand them over to the
secondary CPU.
Thanks,
Ingo
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