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The linux-next integration testing tree
e65a0dc1ca
p9_get_mapped_pages() uses iov_iter_get_pages_alloc2() to extract pages
from an iterator when performing a zero-copy request and under some
circumstances, this crashes with odd page errors[1], for example, I see:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xbcf0
flags: 0x2000000000000000(zone=1)
...
page dumped because: VM_BUG_ON_FOLIO(((unsigned int) folio_ref_count(folio) + 127u <= 127u))
------------[ cut here ]------------
kernel BUG at include/linux/mm.h:1444!
This is because, unlike in iov_iter_extract_folioq_pages(), the
iter_folioq_get_pages() helper function doesn't skip the current folio
when iov_offset points to the end of it, but rather extracts the next
page beyond the end of the folio and adds it to the list. Reading will
then clobber the contents of this page, leading to system corruption,
and if the page is not in use, put_page() may try to clean up the unused
page.
This can be worked around by copying the iterator before each
extraction[2] and using iov_iter_advance() on the original as the
advance function steps over the page we're at the end of.
Fix this by skipping the page extraction if we're at the end of the
folio.
This was reproduced in the ktest environment[3] by forcing 9p to use the
fscache caching mode and then reading a file through 9p.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| 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 reStructuredText 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.