__blkdev_put() could surprise writeback thread by detaching the
wb object from an inode that hasn't cleared the I_SYNC flag yet.
This causes a NULL pointer dereference as seen below:
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: locked_inode_to_wb_and_lock_list+0x38/0x440
PGD 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 34 Comm: kworker/u8:1 Not tainted 4.11.0-rc1+ #202
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: writeback wb_workfn (flush-8:16)
task: ffff88013aa780c0 task.stack: ffffc9000012c000
RIP: 0010:locked_inode_to_wb_and_lock_list+0x38/0x440
RSP: 0018:ffffc9000012fb70 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000018
RDX: ffff88013aa780c0 RSI: ffff880139a478f8 RDI: ffff88013aa788b8
RBP: ffffc9000012fba0 R08: 0000000000000001 R09: 0000000000000000
R10: 00000000969da8e2 R11: 0000000000000000 R12: ffff880139a47858
R13: ffff880139a478e0 R14: ffff880139a478f8 R15: ffff8801371f4058
FS: 0000000000000000(0000) GS:ffff88013ae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000001012000 CR4: 00000000000006f0
Call Trace:
writeback_sb_inodes+0x3e1/0x7a0
__writeback_inodes_wb+0x87/0xc0
wb_writeback+0x2e7/0x5c0
wb_workfn+0x2d1/0x9c0
process_one_work+0x1d3/0x620
worker_thread+0x126/0x4a0
kthread+0x10a/0x140
ret_from_fork+0x2e/0x40
RIP: locked_inode_to_wb_and_lock_list+0x38/0x440 RSP: ffffc9000012fb70
CR2: 0000000000000000
---[ end trace e0ea8a2695f4c86c ]---
Make __blkdev_put() wait for the I_SYNC flag to clear before detaching
wb.
Fixes: 43d1c0eb7e11 ("block: detach bdev inode from its wb in __blkdev_put()")
Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>
---
v2:
Removed white space clean up changes
fs/block_dev.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2eca00ec4370..fdc71f9f8003 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1880,7 +1880,10 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
* Detaching bdev inode from its wb in __destroy_inode()
* is too late: the queue which embeds its bdi (along with
* root wb) can be gone as soon as we put_disk() below.
+ * Before detaching wb, wait for any writeback activity for
+ * inode to settle.
*/
+ inode_wait_for_writeback(bdev->bd_inode);
inode_detach_wb(bdev->bd_inode);
}
if (bdev->bd_contains == bdev) {
--
2.12.0.246.ga2ecc84866-goog