From cccd32816506cbac3a4c65d9dff51b3125ef1a03 Mon Sep 17 00:00:00 2001 From: Lukas Wunner Date: Fri, 15 Sep 2023 09:55:39 +0200 Subject: panic: Reenable preemption in WARN slowpath Commit: 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG") amended warn_slowpath_fmt() to disable preemption until the WARN splat has been emitted. However the commit neglected to reenable preemption in the !fmt codepath, i.e. when a WARN splat is emitted without additional format string. One consequence is that users may see more splats than intended. E.g. a WARN splat emitted in a work item results in at least two extra splats: BUG: workqueue leaked lock or atomic (emitted by process_one_work()) BUG: scheduling while atomic (emitted by worker_thread() -> schedule()) Ironically the point of the commit was to *avoid* extra splats. ;) Fix it. Fixes: 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG") Signed-off-by: Lukas Wunner Signed-off-by: Ingo Molnar Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Paul E. McKenney Link: https://lore.kernel.org/r/3ec48fde01e4ee6505f77908ba351bad200ae3d1.1694763684.git.lukas@wunner.de --- kernel/panic.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/panic.c') diff --git a/kernel/panic.c b/kernel/panic.c index 07239d4ad81e..ffa037fa777d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -697,6 +697,7 @@ void warn_slowpath_fmt(const char *file, int line, unsigned taint, if (!fmt) { __warn(file, line, __builtin_return_address(0), taint, NULL, NULL); + warn_rcu_exit(rcu); return; } -- cgit v1.2.3 From 9734fe4dc22052d8010cc0b68b092fe5335ccb31 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Mon, 4 Sep 2023 17:21:01 +0200 Subject: panic: use atomic_try_cmpxchg in panic() and nmi_panic() Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in panic() and nmi_panic(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, rename cpu variable to this_cpu in nmi_panic() and try to unify logic flow between panic() and nmi_panic(). No functional change intended. [ubizjak@gmail.com: clean up if/else block] Link: https://lkml.kernel.org/r/20230906191200.68707-1-ubizjak@gmail.com Link: https://lkml.kernel.org/r/20230904152230.9227-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Cc: Mark Rutland Signed-off-by: Andrew Morton --- kernel/panic.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) (limited to 'kernel/panic.c') diff --git a/kernel/panic.c b/kernel/panic.c index ffa037fa777d..2807639aab51 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -192,14 +192,15 @@ atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID); */ void nmi_panic(struct pt_regs *regs, const char *msg) { - int old_cpu, cpu; + int old_cpu, this_cpu; - cpu = raw_smp_processor_id(); - old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu); + old_cpu = PANIC_CPU_INVALID; + this_cpu = raw_smp_processor_id(); - if (old_cpu == PANIC_CPU_INVALID) + /* atomic_try_cmpxchg updates old_cpu on failure */ + if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) panic("%s", msg); - else if (old_cpu != cpu) + else if (old_cpu != this_cpu) nmi_panic_self_stop(regs); } EXPORT_SYMBOL(nmi_panic); @@ -311,15 +312,18 @@ void panic(const char *fmt, ...) * stop themself or will wait until they are stopped by the 1st CPU * with smp_send_stop(). * - * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which - * comes here, so go ahead. + * cmpxchg success means this is the 1st CPU which comes here, + * so go ahead. * `old_cpu == this_cpu' means we came from nmi_panic() which sets * panic_cpu to this CPU. In this case, this is also the 1st CPU. */ + old_cpu = PANIC_CPU_INVALID; this_cpu = raw_smp_processor_id(); - old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); - if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu) + /* atomic_try_cmpxchg updates old_cpu on failure */ + if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) { + /* go ahead */ + } else if (old_cpu != this_cpu) panic_smp_self_stop(); console_verbose(); -- cgit v1.2.3