3.14.61-rt63-rc1 stable review patch.
If anyone has any objections, please let me know.
------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
I see here large latencies during a stack dump on x86. The
preempt_disable() and get_cpu() should forbid moving the task to another
CPU during a stack dump and avoiding two stack traces in parallel on the
same CPU. However a stack trace from a second CPU may still happen in
parallel. Also nesting is allowed so a stack trace happens in
process-context and we may have another one from IRQ context. With migrate
disable we keep this code preemptible and allow a second backtrace on
the same CPU by another task.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
arch/x86/kernel/dumpstack_64.c | 8 ++++----
lib/dump_stack.c | 4 ++--
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 66e274a3d968..37aee503a7ba 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -114,7 +114,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
unsigned long *stack, unsigned long bp,
const struct stacktrace_ops *ops, void *data)
{
- const unsigned cpu = get_cpu();
+ const unsigned cpu = get_cpu_light();
unsigned long *irq_stack_end =
(unsigned long *)per_cpu(irq_stack_ptr, cpu);
unsigned used = 0;
@@ -191,7 +191,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
* This handles the process stack:
*/
bp = ops->walk_stack(tinfo, stack, bp, ops, data, NULL, &graph);
- put_cpu();
+ put_cpu_light();
}
EXPORT_SYMBOL(dump_trace);
@@ -205,7 +205,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
int cpu;
int i;
- preempt_disable();
+ migrate_disable();
cpu = smp_processor_id();
irq_stack_end = (unsigned long *)(per_cpu(irq_stack_ptr, cpu));
@@ -238,7 +238,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
pr_cont(" %016lx", *stack++);
touch_nmi_watchdog();
}
- preempt_enable();
+ migrate_enable();
pr_cont("\n");
show_trace_log_lvl(task, regs, sp, bp, log_lvl);
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index f23b63f0a1c3..b39c60b1f12c 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -33,7 +33,7 @@ asmlinkage void dump_stack(void)
* Permit this cpu to perform nested stack dumps while serialising
* against other CPUs
*/
- preempt_disable();
+ migrate_disable();
retry:
cpu = smp_processor_id();
@@ -52,7 +52,7 @@ retry:
if (!was_locked)
atomic_set(&dump_lock, -1);
- preempt_enable();
+ migrate_enable();
}
#else
asmlinkage void dump_stack(void)
--
2.7.0
--
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