mm/memory-failure: prioritize prctl(PR_MCE_KILL) over vm.memory_failure_early_kill

Patch series "hwpoison: fixes signaling on memory error"

This is a small patchset to solve issues in memory error handler to send
SIGBUS to proper process/thread as expected in configuration.  Please
see descriptions in individual patches for more details.

This patch (of 2):

Early-kill policy is controlled from two types of settings, one is
per-process setting prctl(PR_MCE_KILL) and the other is system-wide
setting vm.memory_failure_early_kill.  Users expect per-process setting
to override system-wide setting as many other settings do, but
early-kill setting doesn't work as such.

For example, if a system configures vm.memory_failure_early_kill to 1
(enabled), a process receives SIGBUS even if it's configured to
explicitly disable PF_MCE_KILL by prctl().  That's not desirable for
applications with their own policies.

This patch is suggesting to change the priority of these two types of
settings, by checking sysctl_memory_failure_early_kill only when a given
process has the default kill policy.

Note that this patch is solving a thread choice issue too.

Originally, collect_procs() always chooses the main thread when
vm.memory_failure_early_kill is 1, even if the process has a dedicated
thread for memory error handling.  SIGBUS should be sent to the
dedicated thread if early-kill is enabled via
vm.memory_failure_early_kill as we are doing for PR_MCE_KILL_EARLY
processes.

Signed-off-by: Naoya Horiguchi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Pankaj Gupta <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

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