From 074d72ff57f65de779e2f70d5906964c0ba1c123 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Wed, 8 May 2013 12:13:03 -0400 Subject: [PATCH] x86/microcode: Add local mutex to fix physical CPU hot-add deadlock This can easily be triggered if a new CPU is added (via ACPI hotplug mechanism) and from user-space you do: echo 1 > /sys/devices/system/cpu/cpu3/online (or wait for UDEV to do it) on a newly appeared physical 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 lockdep 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: [] cpu_hotplug_driver_lock+0x12/0x20 but task is already holding lock: (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [] 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: [] vfs_write+0x17d/0x190 #1: (&buffer->mutex){+.+.+.}, at: [] sysfs_write_file+0x3f/0x160 #2: (s_active#20){.+.+.+}, at: [] sysfs_write_file+0xc8/0x160 #3: (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [] cpu_hotplug_driver_lock+0x12/0x20 #4: (cpu_add_remove_lock){+.+.+.}, at: [] cpu_maps_update_begin+0x12/0x20 #5: (cpu_hotplug.lock){+.+.+.}, at: [] cpu_hotplug_begin+0x27/0x60 Suggested-and-Acked-by: Borislav Petkov Signed-off-by: Konrad Rzeszutek Wilk Cc: fenghua.yu@intel.com Cc: xen-devel@lists.xensource.com Cc: stable@vger.kernel.org # for v3.9 Link: http://lkml.kernel.org/r/1368029583-23337-1-git-send-email-konrad.wilk@oracle.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/microcode_intel_early.c | 5 +++-- 1 file 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. */ - 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; } -- 2.7.4