d9bb77d51e
[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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.