block: Fix oops in locked_inode_to_wb_and_lock_list()

When block device is closed, we call inode_detach_wb() in __blkdev_put()
which sets inode->i_wb to NULL. That is contrary to expectations that
inode->i_wb stays valid once set during the whole inode's lifetime and
leads to oops in wb_get() in locked_inode_to_wb_and_lock_list() because
inode_to_wb() returned NULL.

The reason why we called inode_detach_wb() is not valid anymore though.
BDI is guaranteed to stay along until we call bdi_put() from
bdev_evict_inode() so we can postpone calling inode_detach_wb() to that
moment.

Also add a warning to catch if someone uses inode_detach_wb() in a
dangerous way.

Reported-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 53e2389ae4d4e7902de07a67cf4814a4d6553496..f2d59f143ef4df875ebd3458153cd31425c92fa9 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -885,6 +885,8 @@ static void bdev_evict_inode(struct inode *inode)
        spin_lock(&bdev_lock);
        list_del_init(&bdev->bd_list);
        spin_unlock(&bdev_lock);
+       /* Detach inode from wb early as bdi_put() may free bdi->wb */
+       inode_detach_wb(inode);
        if (bdev->bd_bdi != &noop_backing_dev_info) {
                bdi_put(bdev->bd_bdi);
                bdev->bd_bdi = &noop_backing_dev_info;
@@ -1875,12 +1877,6 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
                kill_bdev(bdev);
 
                bdev_write_inode(bdev);
-               /*
-                * 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.
-                */
-               inode_detach_wb(bdev->bd_inode);
        }
        if (bdev->bd_contains == bdev) {
                if (disk->fops->release)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index a3c0cbd7c88824a297cd725e36c931c223c3e106..d5815794416c9b8430c7ca9153e3be3271a76899 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -237,6 +237,7 @@ static inline void inode_attach_wb(struct inode *inode, struct page *page)
 static inline void inode_detach_wb(struct inode *inode)
 {
        if (inode->i_wb) {
+               WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
                wb_put(inode->i_wb);
                inode->i_wb = NULL;
        }