Messages in this thread Patch in this message | | | From | Petr Mladek <> | Subject | [PATCH] printk: Make console tracepoint safe in NMI() context | Date | Fri, 15 Jul 2022 14:01:52 +0200 |
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The commit 701850dc0c31bfadf75a0 ("printk, tracing: fix console tracepoint") moved the tracepoint from console_unlock() to vprintk_store(). As a result, it might be called in any context and triggered the following warning:
WARNING: CPU: 1 PID: 16462 at include/trace/events/printk.h:10 printk_sprint+0x81/0xda Modules linked in: ppdev parport_pc parport CPU: 1 PID: 16462 Comm: event_benchmark Not tainted 5.19.0-rc5-test+ #5 Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014 EIP: printk_sprint+0x81/0xda Code: 89 d8 e8 88 fc 33 00 e9 02 00 00 00 eb 6b 64 a1 a4 b8 91 c1 e8 fd d6 ff ff 84 c0 74 5c 64 a1 14 08 92 c1 a9 00 00 f0 00 74 02 <0f> 0b 64 ff 05 14 08 92 c1 b8 e0 c4 6b c1 e8 a5 dc 00 00 89 c7 e8 EAX: 80110001 EBX: c20a52f8 ECX: 0000000c EDX: 6d203036 ESI: 3df6004c EDI: 00000000 EBP: c61fbd7c ESP: c61fbd70 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010006 CR0: 80050033 CR2: b7efc000 CR3: 05b80000 CR4: 001506f0 Call Trace: vprintk_store+0x24b/0x2ff vprintk+0x37/0x4d _printk+0x14/0x16 nmi_handle+0x1ef/0x24e ? find_next_bit.part.0+0x13/0x13 ? find_next_bit.part.0+0x13/0x13 ? function_trace_call+0xd8/0xd9 default_do_nmi+0x57/0x1af ? trace_hardirqs_off_finish+0x2a/0xd9 ? to_kthread+0xf/0xf exc_nmi+0x9b/0xf4 asm_exc_nmi+0xae/0x29c
It comes from:
#define __DO_TRACE(name, args, cond, rcuidle) \ [...] /* srcu can't be used from NMI */ \ WARN_ON_ONCE(rcuidle && in_nmi()); \
It might be possible to make srcu working in NMI. But it would be slower on some architectures. It is not worth doing it just because of this tracepoint.
It would be possible to disable this tracepoint in NMI or in rcuidle context. Where the rcuidle context looks more rare and thus more acceptable to be ignored.
Alternative solution would be to move the tracepoint back to console code. But the location is less reliable by definition. Also the synchronization against other tracing messages is much worse.
Let's ignore the tracepoint in rcuidle context as the least evil solution.
Link: https://lore.kernel.org/r/20220712151655.GU1790663@paulmck-ThinkPad-P17-Gen-1
Suggested-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Petr Mladek <pmladek@suse.com> --- include/trace/events/printk.h | 11 ++++++++++- kernel/printk/printk.c | 2 +- 2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/include/trace/events/printk.h b/include/trace/events/printk.h index 13d405b2fd8b..a3ee720f41b5 100644 --- a/include/trace/events/printk.h +++ b/include/trace/events/printk.h @@ -7,11 +7,20 @@ #include <linux/tracepoint.h> -TRACE_EVENT(console, +TRACE_EVENT_CONDITION(console, TP_PROTO(const char *text, size_t len), TP_ARGS(text, len), + /* + * trace_console_rcuidle() is not working in NMI. printk() + * is used more often in NMI than in rcuidle context. + * Choose the less evil solution here. + * + * raw_smp_processor_id() is reliable in rcuidle context. + */ + TP_CONDITION(!rcu_is_idle_cpu(raw_smp_processor_id())), + TP_STRUCT__entry( __dynamic_array(char, msg, len + 1) ), diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index b49c6ff6dca0..bd76a45ecc7f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2108,7 +2108,7 @@ static u16 printk_sprint(char *text, u16 size, int facility, } } - trace_console_rcuidle(text, text_len); + trace_console(text, text_len); return text_len; } -- 2.35.3
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