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author | Amir Goldstein <amir@cellrox.com> | 2014-08-04 19:29:32 +0300 |
---|---|---|
committer | Rom Lemarchand <romlem@google.com> | 2015-08-20 19:06:44 -0700 |
commit | b54e887e201ff194c3561949cad5a5557ce85069 (patch) | |
tree | 51c7365bafdf7bafb1cb747a871e7206a9b35969 | |
parent | 2f6805e0d78d0575da74a7386e50de3c5eda39e9 (diff) |
sysrq: Emergency Remount R/O in reverse order
This change fixes a problem where reboot on Android panics the kernel
almost every time when file systems are mounted over loop devices.
Android reboot command does:
- sync
- echo u > /proc/sysrq-trigger
- syscall_reboot
The problem is with sysrq emergency remount R/O trying to remount-ro
in wrong order.
since /data is re-mounted ro before loop devices, loop device
remount-ro fails to flush the journal and panics the kernel:
EXT4-fs (loop0): Remounting filesystem read-only
EXT4-fs (loop0): previous I/O error to superblock detected
loop: Write error at byte offset 0, length 4096.
Buffer I/O error on device loop0, logical block 0
lost page write due to I/O error on loop0
Kernel panic - not syncing: EXT4-fs panic from previous error
The fix is quite simple. In do_emergency_remount(), use
list_for_each_entry_reverse() on sb list instead of list_for_each_entry().
It makes a lot of sense to umount the file systems in reverse order in
which they were added to sb list.
Change-Id: I4370e39b5873bd16ade5d5f9ddb2704beb02a2bb
Signed-off-by: Amir Goldstein <amir@cellrox.com>
Acked-by: Oren Laadan <orenl@cellrox.com>
-rw-r--r-- | fs/super.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/super.c b/fs/super.c index 80d5cf2ca765..2e69def2167a 100644 --- a/fs/super.c +++ b/fs/super.c @@ -758,7 +758,7 @@ static void do_emergency_remount(struct work_struct *work) struct super_block *sb, *p = NULL; spin_lock(&sb_lock); - list_for_each_entry(sb, &super_blocks, s_list) { + list_for_each_entry_reverse(sb, &super_blocks, s_list) { if (hlist_unhashed(&sb->s_instances)) continue; sb->s_count++; |