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block: Make blk_get_backing_dev_info() safe without open bdev

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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>
This commit is contained in:
Jan Kara 2017-02-02 15:56:52 +01:00 committed by Jens Axboe
parent d03f6cdc1f
commit b1d2dc5659
3 changed files with 11 additions and 5 deletions
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8
block/blk-core.c
View File

@ -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);

7
fs/block_dev.c
View File

@ -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;

1
include/linux/fs.h
View File

@ -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