ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

If a synchronous error is detected as a result of user-space process
triggering a 2-bit uncorrected error, the CPU will take a synchronous
error exception such as Synchronous External Abort (SEA) on Arm64. The
kernel will queue a memory_failure() work which poisons the related
page, unmaps the page, and then sends a SIGBUS to the process, so that
a system wide panic can be avoided.

However, no memory_failure() work will be queued when abnormal
synchronous errors occur. These errors can include situations like
invalid PA, unexpected severity, no memory failure config support,
invalid GUID section, etc. In such a case, the user-space process will
trigger SEA again.  This loop can potentially exceed the platform
firmware threshold or even trigger a kernel hard lockup, leading to a
system reboot.

Fix it by performing a force kill if no memory_failure() work is queued
for synchronous errors.

Signed-off-by: Shuai Xue <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Yazen Ghannam <[email protected]>
Reviewed-by: Jane Chu <[email protected]>
Reviewed-by: Hanjun Guo <[email protected]>
Link: https://patch.msgid.link/[email protected]
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

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