linux/include
Heiko Carstens e81ce1f7ec [PATCH] timer/hrtimer: take per cpu locks in sane order
Doing something like this on a two cpu system

  # echo 0 > /sys/devices/system/cpu/cpu0/online
  # echo 1 > /sys/devices/system/cpu/cpu0/online
  # echo 0 > /sys/devices/system/cpu/cpu1/online

will give me this:

  =======================================================
  [ INFO: possible circular locking dependency detected ]
  2.6.21-rc2-g562aa1d4-dirty #7
  -------------------------------------------------------
  bash/1282 is trying to acquire lock:
   (&cpu_base->lock_key){.+..}, at: [<000000000005f17e>] hrtimer_cpu_notify+0xc6/0x240

  but task is already holding lock:
   (&cpu_base->lock_key#2){.+..}, at: [<000000000005f174>] hrtimer_cpu_notify+0xbc/0x240

  which lock already depends on the new lock.

This happens because we have the following code in kernel/hrtimer.c:

  migrate_hrtimers(int cpu)
  [...]
  old_base = &per_cpu(hrtimer_bases, cpu);
  new_base = &get_cpu_var(hrtimer_bases);
  [...]
  spin_lock(&new_base->lock);
  spin_lock(&old_base->lock);

Which means the spinlocks are taken in an order which depends on which cpu
gets shut down from which other cpu. Therefore lockdep complains that there
might be an ABBA deadlock. Since migrate_hrtimers() gets only called on
cpu hotplug it's safe to assume that it isn't executed concurrently on a

The same problem exists in kernel/timer.c: migrate_timers().

As pointed out by Christian Borntraeger one possible solution to avoid
the locking order complaints would be to make sure that the locks are
always taken in the same order. E.g. by taking the lock of the cpu with
the lower number first.

To achieve this we introduce two new spinlock functions double_spin_lock
and double_spin_unlock which lock or unlock two locks in a given order.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Christian Borntraeger <cborntra@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-05 07:57:53 -08:00
..
acpi Pull bugzilla-7887 into release branch 2007-02-16 22:11:57 -05:00
asm-alpha [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-arm [PATCH] gpio_keys driver shouldn't be ARM-specific 2007-03-05 07:57:51 -08:00
asm-arm26 Storage class should be before const qualifier 2007-02-17 20:11:19 +01:00
asm-avr32 Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm 2007-02-19 13:18:39 -08:00
asm-cris [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-frv [PATCH] FRV: Add some missng lazy MMU hooks for NOMMU mode 2007-03-01 14:53:36 -08:00
asm-generic [PATCH] i386: paravirt CPU hypercall batching mode 2007-02-13 13:26:21 +01:00
asm-h8300 [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-i386 [PATCH] vmi: apic ops 2007-03-05 07:57:52 -08:00
asm-ia64 [PATCH] sched: remove SMT nice 2007-03-05 07:57:51 -08:00
asm-m32r [PATCH] fix sparse warnings from {asm,net}/checksum.h 2007-02-11 10:51:31 -08:00
asm-m68k [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-m68knommu [PATCH] m68knommu: removed include of system.h from bitops 2007-02-09 10:45:33 -08:00
asm-mips [PATCH] sched: remove SMT nice 2007-03-05 07:57:51 -08:00
asm-parisc Merge master.kernel.org:/pub/scm/linux/kernel/git/kyle/parisc-2.6 2007-02-26 12:48:06 -08:00
asm-powerpc [PATCH] sched: remove SMT nice 2007-03-05 07:57:51 -08:00
asm-ppc [POWERPC] ppc: Add support for AMCC Taishan 440GX eval board 2007-02-13 15:35:52 +11:00
asm-s390 [S390] add atomic64_xchg to s390 2007-02-21 10:55:59 +01:00
asm-sh sh: rts7751r2d board updates. 2007-02-15 18:20:52 +09:00
asm-sh64 [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-sparc [SPARC]: Provide 'get_property()' alias for of_get_property(). 2007-03-02 15:22:53 -08:00
asm-sparc64 [SPARC]: Provide 'get_property()' alias for of_get_property(). 2007-03-02 15:22:53 -08:00
asm-um [PATCH] uml: pte_mkread fix 2007-03-01 14:53:38 -08:00
asm-v850 [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
asm-x86_64 [PATCH] clocksource init adjustments (fix bug #7426) 2007-03-05 07:57:53 -08:00
asm-xtensa [PATCH] consolidate line discipline number definitions 2007-02-11 10:51:26 -08:00
crypto
keys
linux [PATCH] timer/hrtimer: take per cpu locks in sane order 2007-03-05 07:57:53 -08:00
math-emu
media V4L/DVB (5271): Add VIDIOC_TRY_ENCODER_CMD and VIDIOC_ENCODER_CMD ioctls. 2007-03-01 13:09:46 -02:00
mtd [MTD] remove unused ecctype,eccsize fields from struct mtd_info 2007-02-09 15:27:12 +00:00
net [NET]: Fix bugs in "Whether sock accept queue is full" checking 2007-03-02 20:37:33 -08:00
pcmcia serial: Add PCMCIA IDs for Quatech DSP-100 dual RS232 adapter. 2007-02-16 15:19:16 -08:00
rdma RDMA/cma: Add multicast communication support 2007-02-16 14:29:07 -08:00
rxrpc
scsi Merge master.kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2007-02-19 13:32:28 -08:00
sound [ALSA] version 1.0.14rc2 2007-02-14 08:42:20 +01:00
video [PATCH] Video: fb, add true ref_count atomicity 2007-02-12 09:48:42 -08:00
Kbuild