4.4-stable review patch. If anyone has any objections, please let me know.
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From: Tom Hromatka tom.hromatka@oracle.com
[ Upstream commit 0107042768658fea9f5f5a9c00b1c90f5dab6a06 ]
On systems with a large number of CPUs, running sysrq-<q> can cause watchdog timeouts. There are two slow sections of code in the sysrq-<q> path in timer_list.c.
1. print_active_timers() - This function is called by print_cpu() and contains a slow goto loop. On a machine with hundreds of CPUs, this loop took approximately 100ms for the first CPU in a NUMA node. (Subsequent CPUs in the same node ran much quicker.) The total time to print all of the CPUs is ultimately long enough to trigger the soft lockup watchdog.
2. print_tickdevice() - This function outputs a large amount of textual information. This function also took approximately 100ms per CPU.
Since sysrq-<q> is not a performance critical path, there should be no harm in touching the nmi watchdog in both slow sections above. Touching it in just one location was insufficient on systems with hundreds of CPUs as occasional timeouts were still observed during testing.
This issue was observed on an Oracle T7 machine with 128 CPUs, but I anticipate it may affect other systems with similarly large numbers of CPUs.
Signed-off-by: Tom Hromatka tom.hromatka@oracle.com Reviewed-by: Rob Gardner rob.gardner@oracle.com Signed-off-by: John Stultz john.stultz@linaro.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/time/timer_list.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/kernel/time/timer_list.c +++ b/kernel/time/timer_list.c @@ -16,6 +16,7 @@ #include <linux/sched.h> #include <linux/seq_file.h> #include <linux/kallsyms.h> +#include <linux/nmi.h>
#include <asm/uaccess.h>
@@ -96,6 +97,9 @@ print_active_timers(struct seq_file *m,
next_one: i = 0; + + touch_nmi_watchdog(); + raw_spin_lock_irqsave(&base->cpu_base->lock, flags);
curr = timerqueue_getnext(&base->active); @@ -207,6 +211,8 @@ print_tickdevice(struct seq_file *m, str { struct clock_event_device *dev = td->evtdev;
+ touch_nmi_watchdog(); + SEQ_printf(m, "Tick Device: mode: %d\n", td->mode); if (cpu < 0) SEQ_printf(m, "Broadcast device\n");