mainlining shenanigans
0cb5950f3f
When defragging we can end up collecting a range for defrag that has
already pages under delalloc (dirty), as long as the respective extent
map for their range is not mapped to a hole, a prealloc extent or
the extent map is from an old generation.
Most of the time that is harmless from a functional perspective at
least, however it can result in a deadlock:
1) At defrag_collect_targets() we find an extent map that meets all
requirements but there's delalloc for the range it covers, and we add
its range to list of ranges to defrag;
2) The defrag_collect_targets() function is called at defrag_one_range(),
after it locked a range that overlaps the range of the extent map;
3) At defrag_one_range(), while the range is still locked, we call
defrag_one_locked_target() for the range associated to the extent
map we collected at step 1);
4) Then finally at defrag_one_locked_target() we do a call to
btrfs_delalloc_reserve_space(), which will reserve data and metadata
space. If the space reservations can not be satisfied right away, the
flusher might be kicked in and start flushing delalloc and wait for
the respective ordered extents to complete. If this happens we will
deadlock, because both flushing delalloc and finishing an ordered
extent, requires locking the range in the inode's io tree, which was
already locked at defrag_collect_targets().
So fix this by skipping extent maps for which there's already delalloc.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.