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free_handle() for a foreign handle may race with inter-page compaction, what can lead to memory corruption. To avoid that, take write lock not read lock in free_handle to be synchronized with __release_z3fold_page(). For example KASAN can detect it: ================================================================== BUG: KASAN: use-after-free in LZ4_decompress_safe+0x2c4/0x3b8 Read of size 1 at addr ffffffc976695ca3 by task GoogleApiHandle/4121 CPU: 0 PID: 4121 Comm: GoogleApiHandle Tainted: P S OE 4.19.81-perf+ #162 Hardware name: Sony Mobile Communications. PDX-203(KONA) (DT) Call trace: LZ4_decompress_safe+0x2c4/0x3b8 lz4_decompress_crypto+0x3c/0x70 crypto_decompress+0x58/0x70 zcomp_decompress+0xd4/0x120 ... Apart from that, initialize zhdr->mapped_count in init_z3fold_page() and remove "newpage" variable because it is not used anywhere. Signed-off-by: Uladzislau Rezki <uladzislau.rezki@sony.com> Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Qian Cai <cai@lca.pw> Cc: Raymond Jennings <shentino@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200520082100.28876-1-vitaly.wool@konsulko.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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.