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[ Upstream commit aa39cc6757 ]
GC task can deadlock in read_cache_page() because it may attempt
to release a page that is actually allocated by another task in
jffs2_write_begin().
The reason is that in jffs2_write_begin() there is a small window
a cache page is allocated for use but not set Uptodate yet.
This ends up with a deadlock between two tasks:
1) A task (e.g. file copy)
- jffs2_write_begin() locks a cache page
- jffs2_write_end() tries to lock "alloc_sem" from
jffs2_reserve_space() <-- STUCK
2) GC task (jffs2_gcd_mtd3)
- jffs2_garbage_collect_pass() locks "alloc_sem"
- try to lock the same cache page in read_cache_page() <-- STUCK
So to avoid this deadlock, hold "alloc_sem" in jffs2_write_begin()
while reading data in a cache page.
Signed-off-by: Kyeong Yoo <kyeong.yoo@alliedtelesis.co.nz>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.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.