From 15b830d4e877ed908c733ab3219801d1026af256 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Tue, 12 Mar 2019 10:38:19 +0100
Subject: [PATCH] ext4: Avoid panic during forced reboot
Patch-mainline: v5.1-rc2
Git-commit: 1dc1097ff60e4105216da7cd0aa99032b039a994
References: bsc#1126356

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@suse.cz>
---
 fs/ext4/super.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -388,6 +388,12 @@ static void ext4_journal_commit_callback
 	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.
  *
@@ -415,7 +421,12 @@ static void ext4_handle_error(struct sup
 		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
@@ -423,8 +434,7 @@ static void ext4_handle_error(struct sup
 		 */
 		smp_wmb();
 		sb->s_flags |= MS_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;