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author | Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> | 2018-09-28 18:53:04 +0900 |
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committer | Petr Mladek <pmladek@suse.com> | 2018-10-02 15:20:50 +0200 |
commit | 884e370ea88c109a3b982f4eb9ecd82510a3a1fe (patch) | |
tree | 32c6738af64901dfba73182f5c4ff253efa183f5 /kernel/printk | |
parent | f92b070f2dc89a8ff1a0cc8b608e20abef894c7d (diff) | |
download | blackbird-op-linux-884e370ea88c109a3b982f4eb9ecd82510a3a1fe.tar.gz blackbird-op-linux-884e370ea88c109a3b982f4eb9ecd82510a3a1fe.zip |
printk: CON_PRINTBUFFER console registration is a bit racy
CON_PRINTBUFFER console registration requires us to do several
preparation steps:
- Rollback console_seq to replay logbuf messages which were already
seen on other consoles;
- Set exclusive_console flag so console_unlock() will ->write() logbuf
messages only to the exclusive_console driver.
The way we do it, however, is a bit racy
logbuf_lock_irqsave(flags);
console_seq = syslog_seq;
console_idx = syslog_idx;
logbuf_unlock_irqrestore(flags);
<< preemption enabled
<< irqs enabled
exclusive_console = newcon;
console_unlock();
We rollback console_seq under logbuf_lock with IRQs disabled, but
we set exclusive_console with local IRQs enabled and logbuf unlocked.
If the system oops-es or panic-s before we set exclusive_console - and
given that we have IRQs and preemption enabled there is such a
possibility - we will re-play all logbuf messages to every registered
console, which may be a bit annoying and time consuming.
Move exclusive_console assignment to the same IRQs-disabled and
logbuf_lock-protected section where we rollback console_seq.
Link: http://lkml.kernel.org/r/20180928095304.9972-1-sergey.senozhatsky@gmail.com
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Diffstat (limited to 'kernel/printk')
-rw-r--r-- | kernel/printk/printk.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index cfaa211a8b54..c5b568c2d167 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2703,14 +2703,18 @@ void register_console(struct console *newcon) logbuf_lock_irqsave(flags); console_seq = syslog_seq; console_idx = syslog_idx; - logbuf_unlock_irqrestore(flags); /* * We're about to replay the log buffer. Only do this to the * just-registered console to avoid excessive message spam to * the already-registered consoles. + * + * Set exclusive_console with disabled interrupts to reduce + * race window with eventual console_flush_on_panic() that + * ignores console_lock. */ exclusive_console = newcon; exclusive_console_stop_seq = console_seq; + logbuf_unlock_irqrestore(flags); } console_unlock(); console_sysfs_notify(); |