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>
074d72ff57