block: Make blk_get_backing_dev_info() safe without open bdev
Currenly blk_get_backing_dev_info() is not safe to be called when the
block device is not open as bdev->bd_disk is NULL in that case. However
inode_to_bdi() uses this function and may be call called from flusher
worker or other writeback related functions without bdev being open
which leads to crashes such as:
[113031.075540] Unable to handle kernel paging request for data at address 0x00000000
[113031.075614] Faulting instruction address: 0xc0000000003692e0
0:mon> t
[c0000000fb65f900] c00000000036cb6c writeback_sb_inodes+0x30c/0x590
[c0000000fb65fa10] c00000000036ced4 __writeback_inodes_wb+0xe4/0x150
[c0000000fb65fa70] c00000000036d33c wb_writeback+0x30c/0x450
[c0000000fb65fb40] c00000000036e198 wb_workfn+0x268/0x580
[c0000000fb65fc50] c0000000000f3470 process_one_work+0x1e0/0x590
[c0000000fb65fce0] c0000000000f38c8 worker_thread+0xa8/0x660
[c0000000fb65fd80] c0000000000fc4b0 kthread+0x110/0x130
[c0000000fb65fe30] c0000000000098f0 ret_from_kernel_thread+0x5c/0x6c
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index d2bba47..6375674 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -110,14 +110,12 @@ void blk_queue_congestion_threshold(struct request_queue *q)
* @bdev: device
*
* Locates the passed device's request queue and returns the address of its
- * backing_dev_info. This function can only be called if @bdev is opened
- * and the return value is never NULL.
+ * backing_dev_info. The return value is never NULL however we may return
+ * &noop_backing_dev_info if the bdev is not currently open.
*/
struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
{
- struct request_queue *q = bdev_get_queue(bdev);
-
- return q->backing_dev_info;
+ return bdev->bd_bdi;
}
EXPORT_SYMBOL(blk_get_backing_dev_info);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index ed6a34b..601b71b 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -884,6 +884,8 @@ static void bdev_evict_inode(struct inode *inode)
spin_lock(&bdev_lock);
list_del_init(&bdev->bd_list);
spin_unlock(&bdev_lock);
+ if (bdev->bd_bdi != &noop_backing_dev_info)
+ bdi_put(bdev->bd_bdi);
}
static const struct super_operations bdev_sops = {
@@ -986,6 +988,7 @@ struct block_device *bdget(dev_t dev)
bdev->bd_contains = NULL;
bdev->bd_super = NULL;
bdev->bd_inode = inode;
+ bdev->bd_bdi = &noop_backing_dev_info;
bdev->bd_block_size = (1 << inode->i_blkbits);
bdev->bd_part_count = 0;
bdev->bd_invalidated = 0;
@@ -1542,6 +1545,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
bdev->bd_disk = disk;
bdev->bd_queue = disk->queue;
bdev->bd_contains = bdev;
+ if (bdev->bd_bdi == &noop_backing_dev_info)
+ bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);
if (!partno) {
ret = -ENXIO;
@@ -1637,6 +1642,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
bdev->bd_disk = NULL;
bdev->bd_part = NULL;
bdev->bd_queue = NULL;
+ bdi_put(bdev->bd_bdi);
+ bdev->bd_bdi = &noop_backing_dev_info;
if (bdev != bdev->bd_contains)
__blkdev_put(bdev->bd_contains, mode, 1);
bdev->bd_contains = NULL;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 702cb6c..c930cbc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -423,6 +423,7 @@ struct block_device {
int bd_invalidated;
struct gendisk * bd_disk;
struct request_queue * bd_queue;
+ struct backing_dev_info *bd_bdi;
struct list_head bd_list;
/*
* Private data. You must have bd_claim'ed the block_device