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author | Marco Elver <elver@google.com> | 2022-05-03 09:38:44 +0200 |
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committer | Petr Mladek <pmladek@suse.com> | 2022-05-06 10:55:24 +0200 |
commit | 701850dc0c31bfadf75a0a74af7d2c97859945ec (patch) | |
tree | 5e55bba9c194afe9d85a32ffb2cf84c44e69507a /kernel/printk/printk.c | |
parent | ab406816fca009349b89cbde885daf68a8c77e33 (diff) | |
download | linux-701850dc0c31bfadf75a0a74af7d2c97859945ec.tar.gz linux-701850dc0c31bfadf75a0a74af7d2c97859945ec.tar.bz2 linux-701850dc0c31bfadf75a0a74af7d2c97859945ec.zip |
printk, tracing: fix console tracepoint
The original intent of the 'console' tracepoint per the commit 95100358491a
("printk/tracing: Add console output tracing") had been to "[...] record
any printk messages into the trace, regardless of the current console
loglevel. This can help correlate (existing) printk debugging with other
tracing."
Petr points out [1] that calling trace_console_rcuidle() in
call_console_driver() had been the wrong thing for a while, because
"printk() always used console_trylock() and the message was flushed to
the console only when the trylock succeeded. And it was always deferred
in NMI or when printed via printk_deferred()."
With the commit 09c5ba0aa2fc ("printk: add kthread console printers"),
things only got worse, and calls to call_console_driver() no longer
happen with typical printk() calls but always appear deferred [2].
As such, the tracepoint can no longer serve its purpose to clearly
correlate printk() calls and other tracing, as well as breaks usecases
that expect every printk() call to result in a callback of the console
tracepoint. Notably, the KFENCE and KCSAN test suites, which want to
capture console output and assume a printk() immediately gives us a
callback to the console tracepoint.
Fix the console tracepoint by moving it into printk_sprint() [3].
One notable difference is that by moving tracing into printk_sprint(),
the 'text' will no longer include the "header" (loglevel and timestamp),
but only the raw message. Arguably this is less of a problem now that
the console tracepoint happens on the printk() call and isn't delayed.
Link: https://lore.kernel.org/all/Ym+WqKStCg%2FEHfh3@alley/ [1]
Link: https://lore.kernel.org/all/CA+G9fYu2kS0wR4WqMRsj2rePKV9XLgOU1PiXnMvpT+Z=c2ucHA@mail.gmail.com/ [2]
Link: https://lore.kernel.org/all/87fslup9dx.fsf@jogness.linutronix.de/ [3]
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Marco Elver <elver@google.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: John Ogness <john.ogness@linutronix.de>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220503073844.4148944-1-elver@google.com
Diffstat (limited to 'kernel/printk/printk.c')
-rw-r--r-- | kernel/printk/printk.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index f66d6e72a642..a3e1035929b0 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2064,8 +2064,6 @@ static void call_console_driver(struct console *con, const char *text, size_t le { size_t dropped_len; - trace_console_rcuidle(text, len); - if (con->dropped && dropped_text) { dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX, "** %lu printk messages dropped **\n", @@ -2240,6 +2238,8 @@ static u16 printk_sprint(char *text, u16 size, int facility, } } + trace_console_rcuidle(text, text_len); + return text_len; } |