Messages in this thread | | | Date | Thu, 28 May 2015 09:20:10 +0800 | From | Gu Zheng <> | Subject | Re: [RFC PATCH] x86, espfix: postpone the initialization of espfix stack for AP |
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ping...
On 05/22/2015 06:13 PM, Gu Zheng wrote:
> The following lockdep warning occurs when running with 4.1.0-rc3: > [ 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 we could allocate them on the boot CPU side and hand them over to > the secondary CPU, but it seems a waste if some of cpus are still offline. > As there is no need to these pages(espfix stack) until we try to run user > code, so we can postpone the initialization of espfix stack after cpu > booted to avoid the noise. > > Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com> > --- > arch/x86/kernel/smpboot.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 50e547e..3ce05de 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -240,13 +240,6 @@ static void notrace start_secondary(void *unused) > check_tsc_sync_target(); > > /* > - * Enable the espfix hack for this CPU > - */ > -#ifdef CONFIG_X86_ESPFIX64 > - init_espfix_ap(); > -#endif > - > - /* > * We need to hold vector_lock so there the set of online cpus > * does not change while we are assigning vectors to cpus. Holding > * this lock ensures we don't half assign or remove an irq from a cpu. > @@ -901,6 +894,13 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) > } > } > > + /* > + * Enable the espfix hack for this CPU > + */ > +#ifdef CONFIG_X86_ESPFIX64 > + init_espfix_ap(); > +#endif > + > /* mark "stuck" area as not stuck */ > *trampoline_status = 0; >
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