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authorSergey Senozhatsky <sergey.senozhatsky.work@gmail.com>2018-09-28 18:53:04 +0900
committerPetr Mladek <pmladek@suse.com>2018-10-02 15:20:50 +0200
commit884e370ea88c109a3b982f4eb9ecd82510a3a1fe (patch)
tree32c6738af64901dfba73182f5c4ff253efa183f5 /kernel/printk
parentf92b070f2dc89a8ff1a0cc8b608e20abef894c7d (diff)
downloadblackbird-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.c6
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();
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