sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Merge ^/head r357270 through r357349.

Reimplement stack capture of running threads on i386 and amd64.

After r355784 the td_oncpu field is no longer synchronized by the thread
lock, so the stack capture interrupt cannot be delievered pre

Reimplement stack capture of running threads on i386 and amd64.

After r355784 the td_oncpu field is no longer synchronized by the thread
lock, so the stack capture interrupt cannot be delievered precisely.
Fix this using a loop which drops the thread lock and restarts if the
wrong thread was sampled from the stack capture interrupt handler.

Change the implementation to use a regular interrupt instead of an NMI.
Now that we drop the thread lock, there is no advantage to the latter.

Simplify the KPIs. Remove stack_save_td_running() and add a return
value to stack_save_td(). On platforms that do not support stack
capture of running threads, stack_save_td() returns EOPNOTSUPP. If the
target thread is running in user mode, stack_save_td() returns EBUSY.

Reviewed by: kib
Reported by: mjg, pho
Tested by: pho
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D23355

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Merge from head

Sponsored by: Gandi.net

Merge from head

Sync up with head (up to r288341).

Finish merging from head, messed up in previous attempt

Merge ^/head r287527 through r287679.

Add stack_save_td_running(), a function to trace the kernel stack of a
running thread.

It is currently implemented only on amd64 and i386; on these
architectures, it is implemented by raising an NMI

Add stack_save_td_running(), a function to trace the kernel stack of a
running thread.

It is currently implemented only on amd64 and i386; on these
architectures, it is implemented by raising an NMI on the CPU on which
the target thread is currently running. Unlike stack_save_td(), it may
fail, for example if the thread is running in user mode.

This change also modifies the kern.proc.kstack sysctl to use this function,
so that stacks of running threads are shown in the output of "procstat -kk".
This is handy for debugging threads that are stuck in a busy loop.

Reviewed by: bdrewery, jhb, kib
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D3256

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Remove the arg0 field from struct amd64_frame. Its existence was a bug,
since on amd64 the first argument to a function is generally not on the
stack.

Revert an old DTrace bug fix to some code that

Remove the arg0 field from struct amd64_frame. Its existence was a bug,
since on amd64 the first argument to a function is generally not on the
stack.

Revert an old DTrace bug fix to some code that assumed that
sizeof(struct amd64_frame) == 16.

Reviewed by: jhb, kib
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D3255

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Merge stack(9) implementations for i386 and amd64 under x86/.

Reviewed by: jhb, kib
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D3255