[PATCH 2/2] bcachefs: only console_trylock in bch2_print_string_as_lines

[Daniel Vetter]

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 at syzkaller.appspotmail.com
References: https://lore.kernel.org/dri-devel/00000000000026c1ff061cd0de12@google.com/
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Fixes: a8f354284304 ("bcachefs: bch2_print_string_as_lines()")
Cc: <stable at vger.kernel.org> # v6.7+
Cc: Kent Overstreet <kent.overstreet at linux.dev>
Cc: Brian Foster <bfoster at redhat.com>
Cc: linux-bcachefs at vger.kernel.org
Cc: Petr Mladek <pmladek at suse.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: John Ogness <john.ogness at linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky at chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.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