* Ilya Dryomov <idryomov@xxxxxxxxx> [2015-11-20 22:22:34]:
> Since 52ebea749aae ("writeback: make backing_dev_info host
> cgroup-specific bdi_writebacks") inode, at some point in its lifetime,
> gets attached to a wb (struct bdi_writeback). Detaching happens on
> evict, in inode_detach_wb() called from __destroy_inode(), and involves
> updating wb.
>
> However, detaching an internal bdev inode from its wb in
> __destroy_inode() is too late. Its bdi and by extension root wb are
> embedded into struct request_queue, which has different lifetime rules
> and can be freed long before the final bdput() is called (can be from
> __fput() of a corresponding /dev inode, through dput() - evict() -
> bd_forget(). bdevs hold onto the underlying disk/queue pair only while
> opened; as soon as bdev is closed all bets are off. In fact,
> disk/queue can be gone before __blkdev_put() even returns:
>
> 1499 static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
> 1500 {
> ...
> 1518 if (bdev->bd_contains == bdev) {
> 1519 if (disk->fops->release)
> 1520 disk->fops->release(disk, mode);
>
> [ Driver puts its references to disk/queue ]
>
> 1521 }
> 1522 if (!bdev->bd_openers) {
> 1523 struct module *owner = disk->fops->owner;
> 1524
> 1525 disk_put_part(bdev->bd_part);
> 1526 bdev->bd_part = NULL;
> 1527 bdev->bd_disk = NULL;
> 1528 if (bdev != bdev->bd_contains)
> 1529 victim = bdev->bd_contains;
> 1530 bdev->bd_contains = NULL;
> 1531
> 1532 put_disk(disk);
>
> [ We put ours, the queue is gone
> The last bdput() would result in a write to invalid memory ]
>
> 1533 module_put(owner);
> ...
> 1539 }
>
> Since bdev inodes are special anyway, detach them in __blkdev_put()
> after clearing inode's dirty bits, turning the problematic
> inode_detach_wb() in __destroy_inode() into a noop.
>
> add_disk() grabs its disk->queue since 523e1d399ce0 ("block: make
> gendisk hold a reference to its queue"), so the old ->release comment
> is removed in favor of the new inode_detach_wb() comment.
>
> Cc: stable@xxxxxxxxxxxxxxx # 4.2+, needs backporting
> Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
> ---
Feel free to add
Tested-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
I was facing bad memory access problem while creating thousands of containers.
With this patch I am able to create more than 10k containers without hitting
the problem.
I had reported the problem here: https://lkml.org/lkml/2015/11/19/149
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