This patch fixes a kernel NULL pointer dereference as mentioned in this log:
---8<---
[ 43.044000] mmc0: card c556 removed
[ 43.059000] mmcblk0: error -123 sending status comand
[ 43.064000] mmcblk0: error -123 sending read/write command, response 0x0, card status 0x0
[ 43.089000] mmcblk0: error -123 requesting status
[ 43.096000] end_request: I/O error, dev mmcblk0, sector 1667989
<snip repeated error>
[ 43.830000] end_request: I/O error, dev mmcblk0, sector 1667988
[ 44.679000] Unable to handle kernel NULL pointer dereference at virtual address 00000010
[ 44.688000] ptbr = 93ec0000 pgd = 93ebf000
[ 44.692000] Oops: Kernel access of bad area, sig: 11 [#1]
[ 44.692000] FRAME_POINTER chip: 0x01f:0x1e82 rev 2
[ 44.692000] Modules linked in:
[ 44.692000] PC is at __mark_inode_dirty+0x8a/0x11c
[ 44.692000] LR is at __mark_inode_dirty+0x7c/0x11c
<snip stack trace>
[ 44.692000] Call trace:
[ 44.692000] [<900780a4>] file_update_time+0x96/0xaa
[ 44.692000] [<9005439a>] __generic_file_aio_write+0x212/0x330
[ 44.692000] [<900544f4>] generic_file_aio_write+0x3c/0x74
[ 44.692000] [<9006b82c>] do_sync_readv_writev+0x68/0x90
[ 44.692000] [<9006b8c0>] do_readv_writev+0x6c/0x108
[ 44.692000] [<9006b98a>] vfs_writev+0x2e/0x34
[ 44.692000] [<9006be60>] sys_writev+0x2c/0x4c
[ 44.692000] [<90023132>] syscall_return+0x0/0x12
[ 44.692000]
--->8---
The reference to sb->s_bdi may be deleted from mmc_blk_remove() ->
del_gendisk() -> unlink_gendisk() -> bdi_unregister() -> bdi_prune_sb() while
another instance try to write some data to the device.
Signed-off-by: Andreas BieÃmann <biessmann@xxxxxxxxxxxxx>
---
fs/fs-writeback.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index cdbf7ac..96b4b25 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1047,6 +1047,9 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if (!was_dirty) {
bdi = inode_to_bdi(inode);
+ if (!bdi)
+ goto out;
+
if (bdi_cap_writeback_dirty(bdi)) {
WARN(!test_bit(BDI_registered, &bdi->state),
"bdi-%s not registered\n", bdi->name);
--
1.7.2.3
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