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4ad6aa46e1
generic/083 occasionally reproduces a panic caused by an overflow when accessing the bch_folio_sector array of the folio being processed by __bch2_truncate_folio(). The immediate cause of the overflow is that the folio offset is beyond i_size, and therefore the sector index calculation underflows on subtraction of the folio offset. One cause of this is mainly observed on nocow mounts. When nocow is enabled, fallocate performs physical block allocation (as opposed to block reservation in cow mode), which range_has_data() then interprets as valid data that requires partial zeroing on truncate. Therefore, if a post-eof zero range request lands across post-eof preallocated blocks, __bch2_truncate_folio() may actually create a post-eof folio in order to perform zeroing. To avoid this problem, update range_has_data() to filter out unwritten blocks from folio creation and partial zeroing. Even though we should never create folios beyond EOF like this, the mere existence of such folios is not necessarily a fatal error. Fix up the truncate code to warn about this condition and not overflow the sector array and possibly crash the system. The addition of this warning without the corresponding unwritten extent fix has shown that various other fstests are able to reproduce this problem fairly frequently, but often in ways that doesn't necessarily result in a kernel panic or a change in user observable behavior, and therefore the problem goes undetected. Signed-off-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev> |
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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.