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Currently memory_failure() is racy against process's exiting, which
results in kernel crash by null pointer dereference.
The root cause is that memory_failure() uses force_sig() to forcibly
kill asynchronous (meaning not in the current context) processes. As
discussed in thread https://lkml.org/lkml/2010/6/8/236 years ago for OOM
fixes, this is not a right thing to do. OOM solves this issue by using
do_send_sig_info() as done in commit d2d393099d ("signal:
oom_kill_task: use SEND_SIG_FORCED instead of force_sig()"), so this
patch is suggesting to do the same for hwpoison. do_send_sig_info()
properly accesses to siglock with lock_task_sighand(), so is free from
the reported race.
I confirmed that the reported bug reproduces with inserting some delay
in kill_procs(), and it never reproduces with this patch.
Note that memory_failure() can send another type of signal using
force_sig_mceerr(), and the reported race shouldn't happen on it because
force_sig_mceerr() is called only for synchronous processes (i.e.
BUS_MCEERR_AR happens only when some process accesses to the corrupted
memory.)
Link: http://lkml.kernel.org/r/20190116093046.GA29835@hori1.linux.bs1.fc.nec.co.jp
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reported-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.