Avoid lockdep warn by having both lock acquirements sleepable.
BTM also have to go to sleep if lock failed at the first time, otherwise it
will race with tty_open()->tty_lock().
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
drivers/tty/tty_io.c | 35 +++++++++++++++++++++++++++++++----
1 files changed, 31 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b425c79..2b4664d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1098,12 +1098,40 @@ out:
*
* We must still hold the BTM and test the CLOSING flag for the moment.
*/
-
void tty_write_message(struct tty_struct *tty, char *msg)
{
+retry:
if (tty) {
- mutex_lock(&tty->atomic_write_lock);
- tty_lock();
+ /*
+ * tty_write_message() will invoked by print_warning()
+ * at fs/quota/dquot.c if CONFIG_PRINT_QUOTA_WARNING
+ * is enabled when a user running out of disk quota limits.
+ * It will end up call tty_write(). Here is a potential race
+ * situation since tty_write() call copy_from_user() which
+ * might produce page faults and turn to invoke inodes dirty
+ * process on the underlying file systems if needed, and
+ * it will try to acquire JBD/JBD2 lock accordingly. This
+ * might make lockdep unhappy to print dead lock warning.
+ * To solve this issue, we have to go to sleep and relinquish
+ * the CPU power to another process until the atomic_write_lock
+ * became available.
+ */
+ if (!mutex_trylock(&tty->atomic_write_lock)) {
+ DEFINE_WAIT(wait);
+ prepare_to_wait_exclusive(&tty->write_wait, &wait,
+ TASK_INTERRUPTIBLE);
+ schedule();
+ finish_wait(&tty->write_wait, &wait);
+ goto retry;
+ }
+
+ /*
+ * Call tty_lock() directly might race with tty_open() even
+ * if we have already got the atomic_write_lock. However, we
+ * must perform TTY_CLOSING check up with the BTM hold, so call
+ * tty_lock_wait() which is sleepable instead.
+ */
+ tty_lock_wait();
if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
tty_unlock();
tty->ops->write(tty, msg, strlen(msg));
@@ -1114,7 +1142,6 @@ void tty_write_message(struct tty_struct *tty, char *msg)
return;
}
-
/**
* tty_write - write method for tty device file
* @file: tty file pointer
--
1.7.9
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