From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: syzbot <syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
linux-serial <linux-serial@vger.kernel.org>
Subject: [PATCH] tty: vt: check for atomic context in con_write()
Date: Sat, 20 Jan 2024 19:34:02 +0900 [thread overview]
Message-ID: <9cd9d3eb-418f-44cc-afcf-7283d51252d6@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <83414cb6-df16-4b6d-92e3-d54d22ba26cc@I-love.SAKURA.ne.jp>
syzbot is reporting sleep in atomic context, for gsmld_write() is calling
con_write() with spinlock held and IRQs disabled.
Since include/linux/tty_ldisc.h says that "struct tty_ldisc_ops"->write
(e.g. gsmld_write()) is allowed to sleep and include/linux/tty_driver.h
says that "struct tty_operations"->write (e.g. con_write()) is not
allowed to sleep, we should handle this problem on the con_write() side.
It seems that "Andrew Morton: console locking merge" in 2.4.10-pre11 added
in_interrupt() check to do_con_write()/con_put_char()/con_flush_chars()
in order to handle exceptional caller.
Since include/linux/preempt.h says that in_atomic() cannot know about held
spinlocks in non-preemptible kernels, but gsmld_write() is calling
con_write() with IRQs disabled, we can add irqs_disabled() check to
do_con_write()/con_flush_chars() in order to handle this case. Though,
I'm not sure whether returning the bytes to write is appropriate behavior
when do_con_write() can't work...
Reported-by: syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=06fa1063cca8163ea541
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
drivers/tty/vt/vt.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 156efda7c80d..0d3d602ae147 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2856,7 +2856,7 @@ static int do_con_write(struct tty_struct *tty, const u8 *buf, int count)
struct vt_notifier_param param;
bool rescan;
- if (in_interrupt())
+ if (in_interrupt() || irqs_disabled())
return count;
console_lock();
@@ -3314,7 +3314,7 @@ static void con_flush_chars(struct tty_struct *tty)
{
struct vc_data *vc;
- if (in_interrupt()) /* from flush_to_ldisc */
+ if (in_interrupt() || irqs_disabled()) /* from flush_to_ldisc */
return;
/* if we race with con_close(), vt may be null */
--
2.18.4
next prev parent reply other threads:[~2024-01-20 10:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-18 9:51 [syzbot] [dri?] BUG: scheduling while atomic in drm_atomic_helper_wait_for_flip_done syzbot
2024-01-18 14:18 ` Tetsuo Handa
2024-01-20 10:34 ` Tetsuo Handa [this message]
2024-01-21 3:48 ` [PATCH] tty: vt: check for atomic context in con_write() Hillf Danton
2024-01-21 11:34 ` Tetsuo Handa
2024-01-22 6:48 ` Jiri Slaby
2024-01-22 14:08 ` Tetsuo Handa
2024-01-24 10:06 ` [PATCH] tty: n_gsm: restrict tty devices to attach Tetsuo Handa
2024-01-24 13:14 ` Greg Kroah-Hartman
2024-02-03 13:45 ` Tetsuo Handa
2024-02-06 14:28 ` Greg Kroah-Hartman
2024-04-20 11:17 ` [syzbot] [dri?] BUG: scheduling while atomic in drm_atomic_helper_wait_for_flip_done Tetsuo Handa
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