Patch "ext4: avoid panic during forced reboot" has been added to the 5.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ext4: avoid panic during forced reboot

to the 5.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ext4-avoid-panic-during-forced-reboot.patch
and it can be found in the queue-5.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit dbec735b02040c15e86558f7aef51d9f0179de2f
Author: Jan Kara <jack@xxxxxxx>
Date:   Thu Mar 14 23:46:05 2019 -0400

    ext4: avoid panic during forced reboot
    
    [ Upstream commit 1dc1097ff60e4105216da7cd0aa99032b039a994 ]
    
    When admin calls "reboot -f" - i.e., does a hard system reboot by
    directly calling reboot(2) - ext4 filesystem mounted with errors=panic
    can panic the system. This happens because the underlying device gets
    disabled without unmounting the filesystem and thus some syscall running
    in parallel to reboot(2) can result in the filesystem getting IO errors.
    
    This is somewhat surprising to the users so try improve the behavior by
    switching to errors=remount-ro behavior when the system is running
    reboot(2).
    
    Signed-off-by: Jan Kara <jack@xxxxxxx>
    Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fb12d3c17c1b..b9bca7298f96 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -430,6 +430,12 @@ static void ext4_journal_commit_callback(journal_t *journal, transaction_t *txn)
 	spin_unlock(&sbi->s_md_lock);
 }
 
+static bool system_going_down(void)
+{
+	return system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF
+		|| system_state == SYSTEM_RESTART;
+}
+
 /* Deal with the reporting of failure conditions on a filesystem such as
  * inconsistencies detected or read IO failures.
  *
@@ -460,7 +466,12 @@ static void ext4_handle_error(struct super_block *sb)
 		if (journal)
 			jbd2_journal_abort(journal, -EIO);
 	}
-	if (test_opt(sb, ERRORS_RO)) {
+	/*
+	 * We force ERRORS_RO behavior when system is rebooting. Otherwise we
+	 * could panic during 'reboot -f' as the underlying device got already
+	 * disabled.
+	 */
+	if (test_opt(sb, ERRORS_RO) || system_going_down()) {
 		ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
 		/*
 		 * Make sure updated value of ->s_mount_flags will be visible
@@ -468,8 +479,7 @@ static void ext4_handle_error(struct super_block *sb)
 		 */
 		smp_wmb();
 		sb->s_flags |= SB_RDONLY;
-	}
-	if (test_opt(sb, ERRORS_PANIC)) {
+	} else if (test_opt(sb, ERRORS_PANIC)) {
 		if (EXT4_SB(sb)->s_journal &&
 		  !(EXT4_SB(sb)->s_journal->j_flags & JBD2_REC_ERR))
 			return;