diff options
Diffstat (limited to 'Documentation/RCU/stallwarn.txt')
| -rw-r--r-- | Documentation/RCU/stallwarn.txt | 37 |
1 files changed, 17 insertions, 20 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 4259f95c3261..491043fd976f 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -16,12 +16,9 @@ o A CPU looping in an RCU read-side critical section. o A CPU looping with interrupts disabled. -o A CPU looping with preemption disabled. This condition can - result in RCU-sched stalls and, if ksoftirqd is in use, RCU-bh - stalls. +o A CPU looping with preemption disabled. -o A CPU looping with bottom halves disabled. This condition can - result in RCU-sched and RCU-bh stalls. +o A CPU looping with bottom halves disabled. o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel without invoking schedule(). If the looping in the kernel is @@ -87,9 +84,9 @@ o A hardware failure. This is quite unlikely, but has occurred This resulted in a series of RCU CPU stall warnings, eventually leading the realization that the CPU had failed. -The RCU, RCU-sched, RCU-bh, and RCU-tasks implementations have CPU stall -warning. Note that SRCU does -not- have CPU stall warnings. Please note -that RCU only detects CPU stalls when there is a grace period in progress. +The RCU, RCU-sched, and RCU-tasks implementations have CPU stall warning. +Note that SRCU does -not- have CPU stall warnings. Please note that +RCU only detects CPU stalls when there is a grace period in progress. No grace period, no CPU stall warnings. To diagnose the cause of the stall, inspect the stack traces. @@ -172,7 +169,7 @@ it will print a message similar to the following: INFO: rcu_sched detected stalls on CPUs/tasks: 2-...: (3 GPs behind) idle=06c/0/0 softirq=1453/1455 fqs=0 16-...: (0 ticks this GP) idle=81c/0/0 softirq=764/764 fqs=0 - (detected by 32, t=2603 jiffies, g=7073, c=7072, q=625) + (detected by 32, t=2603 jiffies, g=7075, q=625) This message indicates that CPU 32 detected that CPUs 2 and 16 were both causing stalls, and that the stall was affecting RCU-sched. This message @@ -215,11 +212,10 @@ CPU since the last time that this CPU noted the beginning of a grace period. The "detected by" line indicates which CPU detected the stall (in this -case, CPU 32), how many jiffies have elapsed since the start of the -grace period (in this case 2603), the number of the last grace period -to start and to complete (7073 and 7072, respectively), and an estimate -of the total number of RCU callbacks queued across all CPUs (625 in -this case). +case, CPU 32), how many jiffies have elapsed since the start of the grace +period (in this case 2603), the grace-period sequence number (7075), and +an estimate of the total number of RCU callbacks queued across all CPUs +(625 in this case). In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed for each CPU: @@ -266,15 +262,16 @@ If the relevant grace-period kthread has been unable to run prior to the stall warning, as was the case in the "All QSes seen" line above, the following additional line is printed: - kthread starved for 23807 jiffies! g7073 c7072 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 + kthread starved for 23807 jiffies! g7075 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 ->cpu=5 Starving the grace-period kthreads of CPU time can of course result in RCU CPU stall warnings even when all CPUs and tasks have passed -through the required quiescent states. The "g" and "c" numbers flag the -number of the last grace period started and completed, respectively, -the "f" precedes the ->gp_flags command to the grace-period kthread, -the "RCU_GP_WAIT_FQS" indicates that the kthread is waiting for a short -timeout, and the "state" precedes value of the task_struct ->state field. +through the required quiescent states. The "g" number shows the current +grace-period sequence number, the "f" precedes the ->gp_flags command +to the grace-period kthread, the "RCU_GP_WAIT_FQS" indicates that the +kthread is waiting for a short timeout, the "state" precedes value of the +task_struct ->state field, and the "cpu" indicates that the grace-period +kthread last ran on CPU 5. Multiple Warnings From One Stall |