Commit-ID: ce4f06dcbb5d6d04d202f1b81ac72d5679dcdfc0 Gitweb: http://git.kernel.org/tip/ce4f06dcbb5d6d04d202f1b81ac72d5679dcdfc0 Author: Oleg Nesterov <o...@redhat.com> AuthorDate: Tue, 26 Jul 2016 20:57:36 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Wed, 27 Jul 2016 11:12:11 +0200
stop_machine: Touch_nmi_watchdog() after MULTI_STOP_PREPARE Suppose that stop_machine(fn) hangs because fn() hangs. In this case NMI hard-lockup can be triggered on another CPU which does nothing wrong and the trace from nmi_panic() won't help to investigate the problem. And this change "fixes" the problem we (seem to) hit in practice. - stop_two_cpus(0, 1) races with show_state_filter() running on CPU_0. - CPU_1 already spins in MULTI_STOP_PREPARE state, it detects the soft lockup and tries to report the problem. - show_state_filter() enables preemption, CPU_0 calls multi_cpu_stop() which goes to MULTI_STOP_DISABLE_IRQ state and disables interrupts. - CPU_1 spends more than 10 seconds trying to flush the log buffer to the slow serial console. - NMI interrupt on CPU_0 (which now waits for CPU_1) calls nmi_panic(). Reported-by: Wang Shu <shuw...@redhat.com> Signed-off-by: Oleg Nesterov <o...@redhat.com> Reviewed-by: Thomas Gleixner <t...@linutronix.de> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Dave Anderson <ander...@redhat.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Tejun Heo <t...@kernel.org> Link: http://lkml.kernel.org/r/20160726185736.gb4...@redhat.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/stop_machine.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index a467e6c..4a1ca5f 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -21,6 +21,7 @@ #include <linux/smpboot.h> #include <linux/atomic.h> #include <linux/lglock.h> +#include <linux/nmi.h> /* * Structure to determine completion condition and record errors. May @@ -209,6 +210,13 @@ static int multi_cpu_stop(void *data) break; } ack_state(msdata); + } else if (curstate > MULTI_STOP_PREPARE) { + /* + * At this stage all other CPUs we depend on must spin + * in the same loop. Any reason for hard-lockup should + * be detected and reported on their side. + */ + touch_nmi_watchdog(); } } while (curstate != MULTI_STOP_EXIT);
