From: Sergey Senozhatsky sergey.senozhatsky.work@gmail.com
[ Upstream commit 884e370ea88c109a3b982f4eb9ecd82510a3a1fe ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/printk/printk.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index b627954061bb6..11d70fd15e706 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2708,14 +2708,18 @@ 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();