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serial: drop debugging WARN_ON_ONCE() from uart_put_char()

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Pengfei Xu reports, that the -next commit 1788cf6a91 (tty: serial:
switch from circ_buf to kfifo) tries to emit a WARNING and that leads to
lockdep errors. Obviously we cannot print anything from uart_put_char()!

This WARN_ON_ONCE() was/is a debug aid to check if the condition in
uart_put_char() can happen at all. Pengfei Xu confirmed it can. Unlike
me and kbuild bot in my queue.

Second, I completely forgot about it, so I did not remove it in the
final version, nor mentioned it in the commit log.

Drop it now as we are all good. And we even have stack traces (and a
reproducer)!

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Link: https://lore.kernel.org/r/20240416071904.21440-1-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jiri Slaby (SUSE) 2024-04-16 09:19:04 +02:00 committed by Greg Kroah-Hartman
parent 35fad98ed2
commit 5f1149d2f4
1 changed files with 1 additions and 1 deletions
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2
drivers/tty/serial/serial_core.c
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@ -558,7 +558,7 @@ static int uart_put_char(struct tty_struct *tty, u8 c)
int ret = 0;
port = uart_port_lock(state, flags);
if (WARN_ON_ONCE(!state->port.xmit_buf)) {
if (!state->port.xmit_buf) {
uart_port_unlock(port, flags);
return 0;
}