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[ Upstream commit 3bf19a0fb690022ec22ce87a5afeb1030cbcb56c ] When arch_stack_walk_reliable() is called to unwind for newly forked tasks, the return value is negative which means the call stack is unreliable. This obviously does not meet expectations. The root cause is that after commit3aec4ecb3d("x86: Rewrite ret_from_fork() in C"), the 'ret_addr' of newly forked task is changed to 'ret_from_fork_asm' (see copy_thread()), then at the start of the unwind, it is incorrectly interprets not as a "signal" one because 'ret_from_fork' is still used to determine the initial "signal" (see __unwind_start()). Then the address gets incorrectly decremented in the call to orc_find() (see unwind_next_frame()) and resulting in the incorrect ORC data. To fix it, check 'ret_from_fork_asm' rather than 'ret_from_fork' in __unwind_start(). Fixes:3aec4ecb3d("x86: Rewrite ret_from_fork() in C") Signed-off-by: Zheng Yejian <zhengyejian@huaweicloud.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> 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.