RE: [PATCH] x86, microcode: Add local mutex to not hit a deadlock.

Yu, Fenghua
2013-05-15T18:28:28Z

> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
>
> This can easily be triggered if a new CPU is added (via
> ACPI hotplug mechanism) and from user-space do:
>
> echo 1 > /sys/devices/system/cpu/cpu3/online
>
> (or wait for UDEV to do it) on a newly appeared CPU.
>
> The deadlock is that the "store_online" in drivers/base/cpu.c
> takes the cpu_hotplug_driver_lock() lock, then calls "cpu_up".
> "cpu_up" eventually ends up calling "save_mc_for_early"
> which also takes the cpu_hotplug_driver_lock() lock.
>
> And here is that kernel thinks of it:
>
> smpboot: Stack at about ffff880075c39f44
> smpboot: CPU3: has booted.
> microcode: CPU3 sig=0x206a7, pf=0x2, revision=0x25
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.9.0upstream-10129-g167af0e #1 Not tainted
> ---------------------------------------------
> sh/2487 is trying to acquire lock:
> (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>]
> cpu_hotplug_driver_lock+0x12/0x20
>
> but task is already holding lock:
> (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>]
> cpu_hotplug_driver_lock+0x12/0x20
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(x86_cpu_hotplug_driver_mutex);
> lock(x86_cpu_hotplug_driver_mutex);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 6 locks held by sh/2487:
> #0: (sb_writers#5){.+.+.+}, at: [<ffffffff811ca48d>]
> vfs_write+0x17d/0x190
> #1: (&buffer->mutex){+.+.+.}, at: [<ffffffff812464ef>]
> sysfs_write_file+0x3f/0x160
> #2: (s_active#20){.+.+.+}, at: [<ffffffff81246578>]
> sysfs_write_file+0xc8/0x160
> #3: (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff81075512>]
> cpu_hotplug_driver_lock+0x12/0x20
> #4: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff810961c2>]
> cpu_maps_update_begin+0x12/0x20
> #5: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff810962a7>]
> cpu_hotplug_begin+0x27/0x60
>
> Suggested-by: Borislav Petkov <bp@alien8.de>
> CC: stable@vger.kernel.org # for v3.9
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
> arch/x86/kernel/microcode_intel_early.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/microcode_intel_early.c
> b/arch/x86/kernel/microcode_intel_early.c
> index d893e8e..2e9e128 100644
> --- a/arch/x86/kernel/microcode_intel_early.c
> +++ b/arch/x86/kernel/microcode_intel_early.c
> @@ -487,6 +487,7 @@ static inline void show_saved_mc(void)
> #endif
>
> #if defined(CONFIG_MICROCODE_INTEL_EARLY) &&
> defined(CONFIG_HOTPLUG_CPU)
> +static DEFINE_MUTEX(x86_cpu_microcode_mutex);
> /*
> * Save this mc into mc_saved_data. So it will be loaded early when a
> CPU is
> * hot added or resumes.
> @@ -507,7 +508,7 @@ int save_mc_for_early(u8 *mc)
> * Hold hotplug lock so mc_saved_data is not accessed by a CPU in
> * hotplug.
> */

Could you please change the comment to use mutex instead? I think the mutex
is good way to handle race here.

> - cpu_hotplug_driver_lock();
> + mutex_lock(&x86_cpu_microcode_mutex);
>
> mc_saved_count_init = mc_saved_data.mc_saved_count;
> mc_saved_count = mc_saved_data.mc_saved_count;
> @@ -544,7 +545,7 @@ int save_mc_for_early(u8 *mc)
> }
>
> out:
> - cpu_hotplug_driver_unlock();
> + mutex_unlock(&x86_cpu_microcode_mutex);
>
> return ret;
> }
> --
> 1.7.7.6