This is a note to let you know that I've just added the patch titled
x86/microcode: Add local mutex to fix physical CPU hot-add deadlock
to the 3.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-microcode-add-local-mutex-to-fix-physical-cpu-hot-add-deadlock.patch
and it can be found in the queue-3.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 074d72ff57f65de779e2f70d5906964c0ba1c123 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Wed, 8 May 2013 12:13:03 -0400
Subject: x86/microcode: Add local mutex to fix physical CPU hot-add deadlock
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
commit 074d72ff57f65de779e2f70d5906964c0ba1c123 upstream.
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@xxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: fenghua.yu@xxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1368029583-23337-1-git-send-email-konrad.wilk@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/microcode_intel_early.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- 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;
}
Patches currently in stable-queue which might be from konrad.wilk@xxxxxxxxxx are
queue-3.9/xen-vcpu-pvhvm-fix-vcpu-hotplugging-hanging.patch
queue-3.9/x86-microcode-add-local-mutex-to-fix-physical-cpu-hot-add-deadlock.patch
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