path: root/kernel
diff options
authorTirupathi Reddy <tirupath@codeaurora.org>2013-05-14 13:59:02 +0530
committerThomas Gleixner <tglx@linutronix.de>2013-05-14 17:59:18 +0200
commit42a5cf46cd56f46267d2a9fcf2655f4078cd3042 (patch)
treed2f1c59ce75918b53b773e9b702a811e725e4756 /kernel
parentf7ea0fd639c2c48d3c61b6eec75362be290c6874 (diff)
timer: Don't reinitialize the cpu base lock during CPU_UP_PREPARE
An inactive timer's base can refer to a offline cpu's base. In the current code, cpu_base's lock is blindly reinitialized each time a CPU is brought up. If a CPU is brought online during the period that another thread is trying to modify an inactive timer on that CPU with holding its timer base lock, then the lock will be reinitialized under its feet. This leads to following SPIN_BUG(). <0> BUG: spinlock already unlocked on CPU#3, kworker/u:3/1466 <0> lock: 0xe3ebe000, .magic: dead4ead, .owner: kworker/u:3/1466, .owner_cpu: 1 <4> [<c0013dc4>] (unwind_backtrace+0x0/0x11c) from [<c026e794>] (do_raw_spin_unlock+0x40/0xcc) <4> [<c026e794>] (do_raw_spin_unlock+0x40/0xcc) from [<c076c160>] (_raw_spin_unlock+0x8/0x30) <4> [<c076c160>] (_raw_spin_unlock+0x8/0x30) from [<c009b858>] (mod_timer+0x294/0x310) <4> [<c009b858>] (mod_timer+0x294/0x310) from [<c00a5e04>] (queue_delayed_work_on+0x104/0x120) <4> [<c00a5e04>] (queue_delayed_work_on+0x104/0x120) from [<c04eae00>] (sdhci_msm_bus_voting+0x88/0x9c) <4> [<c04eae00>] (sdhci_msm_bus_voting+0x88/0x9c) from [<c04d8780>] (sdhci_disable+0x40/0x48) <4> [<c04d8780>] (sdhci_disable+0x40/0x48) from [<c04bf300>] (mmc_release_host+0x4c/0xb0) <4> [<c04bf300>] (mmc_release_host+0x4c/0xb0) from [<c04c7aac>] (mmc_sd_detect+0x90/0xfc) <4> [<c04c7aac>] (mmc_sd_detect+0x90/0xfc) from [<c04c2504>] (mmc_rescan+0x7c/0x2c4) <4> [<c04c2504>] (mmc_rescan+0x7c/0x2c4) from [<c00a6a7c>] (process_one_work+0x27c/0x484) <4> [<c00a6a7c>] (process_one_work+0x27c/0x484) from [<c00a6e94>] (worker_thread+0x210/0x3b0) <4> [<c00a6e94>] (worker_thread+0x210/0x3b0) from [<c00aad9c>] (kthread+0x80/0x8c) <4> [<c00aad9c>] (kthread+0x80/0x8c) from [<c000ea80>] (kernel_thread_exit+0x0/0x8) As an example, this particular crash occurred when CPU #3 is executing mod_timer() on an inactive timer whose base is refered to offlined CPU #2. The code locked the timer_base corresponding to CPU #2. Before it could proceed, CPU #2 came online and reinitialized the spinlock corresponding to its base. Thus now CPU #3 held a lock which was reinitialized. When CPU #3 finally ended up unlocking the old cpu_base corresponding to CPU #2, we hit the above SPIN_BUG(). CPU #0 CPU #3 CPU #2 ------ ------- ------- ..... ...... <Offline> mod_timer() lock_timer_base spin_lock_irqsave(&base->lock) cpu_up(2) ..... ...... init_timers_cpu() .... ..... spin_lock_init(&base->lock) ..... spin_unlock_irqrestore(&base->lock) ...... <spin_bug> Allocation of per_cpu timer vector bases is done only once under "tvec_base_done[]" check. In the current code, spinlock_initialization of base->lock isn't under this check. When a CPU is up each time the base lock is reinitialized. Move base spinlock initialization under the check. Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1368520142-4136-1-git-send-email-tirupath@codeaurora.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel')
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 09bca8ce977..7376589adc2 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1539,12 +1539,12 @@ static int __cpuinit init_timers_cpu(int cpu)
boot_done = 1;
base = &boot_tvec_bases;
+ spin_lock_init(&base->lock);
tvec_base_done[cpu] = 1;
} else {
base = per_cpu(tvec_bases, cpu);
- spin_lock_init(&base->lock);
for (j = 0; j < TVN_SIZE; j++) {
INIT_LIST_HEAD(base->tv5.vec + j);