linux-kernel - [PATCH 2/2] bcachefs: only console_trylock in bch2_print_string_as

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Message-ID: <20240710093120.732208-2-daniel.vetter@ffwll.ch>
Date: Wed, 10 Jul 2024 11:31:17 +0200
From: Daniel Vetter <daniel.vetter@...ll.ch>
To: DRI Development <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Cc: Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	syzbot+6cebc1af246fe020a2f0@...kaller.appspotmail.com,
	Daniel Vetter <daniel.vetter@...el.com>,
	stable@...r.kernel.org,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Brian Foster <bfoster@...hat.com>,
	linux-bcachefs@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH 2/2] bcachefs: only console_trylock in bch2_print_string_as_lines

console_lock is the outermost subsystem lock for a lot of subsystems,
which means get/put_user must nest within. Which means it cannot be
acquired somewhere deeply nested in other locks, and most definitely
not while holding fs locks potentially needed to resolve faults.

console_trylock is the best we can do here.

Including printk folks since even trylock feels realyl iffy here to
me.

Reported-by: syzbot+6cebc1af246fe020a2f0@...kaller.appspotmail.com
References: https://lore.kernel.org/dri-devel/00000000000026c1ff061cd0de12@google.com/
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
Fixes: a8f354284304 ("bcachefs: bch2_print_string_as_lines()")
Cc: <stable@...r.kernel.org> # v6.7+
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Brian Foster <bfoster@...hat.com>
Cc: linux-bcachefs@...r.kernel.org
Cc: Petr Mladek <pmladek@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
---
 fs/bcachefs/util.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c
index de331dec2a99..02381c653603 100644
--- a/fs/bcachefs/util.c
+++ b/fs/bcachefs/util.c
@@ -255,13 +255,14 @@ void bch2_prt_u64_base2(struct printbuf *out, u64 v)
 void bch2_print_string_as_lines(const char *prefix, const char *lines)
 {
 	const char *p;
+	int locked;
 
 	if (!lines) {
 		printk("%s (null)\n", prefix);
 		return;
 	}
 
-	console_lock();
+	locked = console_trylock();
 	while (1) {
 		p = strchrnul(lines, '\n');
 		printk("%s%.*s\n", prefix, (int) (p - lines), lines);
@@ -269,7 +270,8 @@ void bch2_print_string_as_lines(const char *prefix, const char *lines)
 			break;
 		lines = p + 1;
 	}
-	console_unlock();
+	if (locked)
+		console_unlock();
 }
 
 int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task, unsigned skipnr,
-- 
2.45.2