[BUG]
When running fstests for btrfs subpage read-write test, it has a very
high chance to crash at generic/475 with the following stack:
BTRFS warning (device dm-8): direct IO failed ino 510 rw 1,34817 sector 0xcdf0 len 94208 err no 10
Unable to handle kernel paging request at virtual address ffff80001157e7c0
CPU: 2 PID: 687125 Comm: kworker/u12:4 Tainted: G WC 5.12.0-rc2-custom+ #5
Hardware name: Khadas VIM3 (DT)
Workqueue: btrfs-endio-meta btrfs_work_helper [btrfs]
pc : queued_spin_lock_slowpath+0x1a0/0x390
lr : do_raw_spin_lock+0xc4/0x11c
Call trace:
queued_spin_lock_slowpath+0x1a0/0x390
_raw_spin_lock+0x68/0x84
btree_readahead_hook+0x38/0xc0 [btrfs]
end_bio_extent_readpage+0x504/0x5f4 [btrfs]
bio_endio+0x170/0x1a4
end_workqueue_fn+0x3c/0x60 [btrfs]
btrfs_work_helper+0x1b0/0x1b4 [btrfs]
process_one_work+0x22c/0x430
worker_thread+0x70/0x3a0
kthread+0x13c/0x140
ret_from_fork+0x10/0x30
Code: 910020e0 8b0200c2 f861d884 aa0203e1 (f8246827)
[CAUSE]
In end_bio_extent_readpage(), if we hit an error during read, we will
handle the error differently for data and metadata.
For data we queue a repair, while for metadata, we record the error and
let the caller choose what to do.
But the code is still using page->private to grab extent buffer, which
no longer points to extent buffer for subpage metadata pages.
Thus this wild pointer access leads to above crash.
[FIX]
Introduce a helper, find_extent_buffer_readpage(), to grab extent
buffer.
The difference against find_extent_buffer_nospinlock() is:
- Also handles regular sectorsize == PAGE_SIZE case
- No extent buffer refs increase/decrease
As extent buffer under IO must have non-zero refs, so this is safe
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
d9bb77d51e