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+coredump selftest
+=================
+
+Background context
+------------------
+
+`coredump` is a feature which dumps a process's memory space when the process terminates
+unexpectedly (e.g. due to segmentation fault), which can be useful for debugging. By default,
+`coredump` dumps the memory to the file named `core`, but this behavior can be changed by writing a
+different file name to `/proc/sys/kernel/core_pattern`. Furthermore, `coredump` can be piped to a
+user-space program by writing the pipe symbol (`|`) followed by the command to be executed to
+`/proc/sys/kernel/core_pattern`. For the full description, see `man 5 core`.
+
+The piped user program may be interested in reading the stack pointers of the crashed process. The
+crashed process's stack pointers can be read from `procfs`: it is the `kstkesp` field in
+`/proc/$PID/stat`. See `man 5 proc` for all the details.
+
+The problem
+-----------
+While a thread is active, the stack pointer is unsafe to read and therefore the `kstkesp` field
+reads zero. But when the thread is dead (e.g. during a coredump), this field should have valid
+value.
+
+However, this was broken in the past and `kstkesp` was zero even during coredump:
+
+* commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in /proc/PID/stat") changed kstkesp to
+  always be zero
+
+* commit fd7d56270b52 ("fs/proc: Report eip/esp in /prod/PID/stat for coredumping") fixed it for the
+  coredumping thread. However, other threads in a coredumping process still had the problem.
+
+* commit cb8f381f1613 ("fs/proc/array.c: allow reporting eip/esp for all coredumping threads") fixed
+  for all threads in a coredumping process.
+
+* commit 92307383082d ("coredump:  Don't perform any cleanups before dumping core") broke it again
+  for the other threads in a coredumping process.
+
+The problem has been fixed now, but considering the history, it may appear again in the future.
+
+The goal of this test
+---------------------
+This test detects problem with reading `kstkesp` during coredump by doing the following:
+
+#. Tell the kernel to execute the "stackdump" script when a coredump happens. This script
+   reads the stack pointers of all threads of crashed processes.
+
+#. Spawn a child process who creates some threads and then crashes.
+
+#. Read the output from the "stackdump" script, and make sure all stack pointer values are
+   non-zero.