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b595d25996
We have been consistently seeing hangs with generic/648 in our subpage GitHub CI setup. This is a classic deadlock, we are calling btrfs_read_folio() on a folio, which requires holding the folio lock on the folio, and then finding a ordered extent that overlaps that range and calling btrfs_start_ordered_extent(), which then tries to write out the dirty page, which requires taking the folio lock and then we deadlock. The hang happens because we're writing to range [1271750656, 1271767040), page index [77621, 77622], and page 77621 is !Uptodate. It is also Dirty, so we call btrfs_read_folio() for 77621 and which does btrfs_lock_and_flush_ordered_range() for that range, and we find an ordered extent which is [1271644160, 1271746560), page index [77615, 77621]. The page indexes overlap, but the actual bytes don't overlap. We're holding the page lock for 77621, then call btrfs_lock_and_flush_ordered_range() which tries to flush the dirty page, and tries to lock 77621 again and then we deadlock. The byte ranges do not overlap, but with subpage support if we clear uptodate on any portion of the page we mark the entire thing as not uptodate. We have been clearing page uptodate on write errors, but no other file system does this, and is in fact incorrect. This doesn't hurt us in the !subpage case because we can't end up with overlapped ranges that don't also overlap on the page. Fix this by not clearing uptodate when we have a write error. The only thing we should be doing in this case is setting the mapping error and carrying on. This makes it so we would no longer call btrfs_read_folio() on the page as it's uptodate and eliminates the deadlock. With this patch we're now able to make it through a full fstests run on our subpage blocksize VMs. Note for stable backports: this probably goes beyond 6.1 but the code has been cleaned up and clearing the uptodate bit must be verified on each version independently. CC: stable@vger.kernel.org # 6.1+ Reviewed-by: Qu Wenruo <wqu@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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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.