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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: [<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-and-Acked-by: Borislav Petkov <bp@alien8.de> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> 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 <mingo@kernel.org>
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parent
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commit
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1 changed files with 3 additions and 2 deletions
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@ -487,6 +487,7 @@ static inline void show_saved_mc(void)
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#endif
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#endif
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#if defined(CONFIG_MICROCODE_INTEL_EARLY) && defined(CONFIG_HOTPLUG_CPU)
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#if defined(CONFIG_MICROCODE_INTEL_EARLY) && defined(CONFIG_HOTPLUG_CPU)
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static DEFINE_MUTEX(x86_cpu_microcode_mutex);
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/*
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/*
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* Save this mc into mc_saved_data. So it will be loaded early when a CPU is
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* Save this mc into mc_saved_data. So it will be loaded early when a CPU is
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* hot added or resumes.
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* hot added or resumes.
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@ -507,7 +508,7 @@ int save_mc_for_early(u8 *mc)
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* Hold hotplug lock so mc_saved_data is not accessed by a CPU in
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* Hold hotplug lock so mc_saved_data is not accessed by a CPU in
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* hotplug.
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* hotplug.
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*/
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*/
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cpu_hotplug_driver_lock();
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mutex_lock(&x86_cpu_microcode_mutex);
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mc_saved_count_init = mc_saved_data.mc_saved_count;
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mc_saved_count_init = mc_saved_data.mc_saved_count;
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mc_saved_count = mc_saved_data.mc_saved_count;
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mc_saved_count = mc_saved_data.mc_saved_count;
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@ -544,7 +545,7 @@ int save_mc_for_early(u8 *mc)
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}
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}
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out:
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out:
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cpu_hotplug_driver_unlock();
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mutex_unlock(&x86_cpu_microcode_mutex);
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return ret;
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return ret;
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}
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}
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