Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use a safer mechanism for determining if a task is currently running,
that does not rely on the lifetime of pointers being the same. This also
restores the task KBI.

Suggested by: jhb
MFC after: 1 month

Fix taskqueue_drain(9) to not have false negatives. For threaded
taskqueues, more than one task can be running simultaneously.

Also make taskqueue_run(9) static to the file, since there are no
consumers in the base kernel and the function signature needs to change
with this fix.

Remove mention of taskqueue_run(9) and taskqueue_run_fast(9) from the
taskqueue(9) man page.

Reviewed by: jhb
Approved by: zml (mentor)

Revert taskqueue(9) related commits until mdf@ is approved and can
resolve issues.

This reverts commits r207439, r208623, r208624

Revert r207439 and solve the problem differently. The task handler
ta_func may free the task structure, so no references to its members
are valid after the handler has been called. Using a per-queue member
and having waits longer than strictly necessary was suggested by jhb.

Submitted by: Matthew Fleming <matthew.fleming@isilon.com>
Reviewed by: zml, jhb

Handle taskqueue_drain(9) correctly on a threaded taskqueue:

taskqueue_drain(9) will not correctly detect whether a task is
currently running. The check is against a field in the taskqueue
struct, but for a threaded queue with more than one thread, multiple
threads can simultaneously be running a task, thus stomping over the
tq_running field.

Submitted by: Matthew Fleming <matthew.fleming@isilon.com>
Reviewed by: jhb
Approved by: dfr (mentor)

revert changes accidentally included in last commit

import vendor fixes to cxgb

o eliminate modification of task structures after their run to avoid
modify-after-free races when the task structure is malloc'd
o shrink task structure by removing ta_flags (no longer needed with
avoid fix) and combining ta_pending and ta_priority

Reviewed by: dwhite, dfr
MFC after: 4 days

Add taskqueue_drain. This waits for the specified task to finish, if
running, or returns. The calling program is responsible for making sure
that nothing new is enqueued.

# man page coming soon.

Remove (at least temporarily) the check that prevents us from including
this file from userland. Since we export struct ifnet to userland, and
that struct ifnet now contains a struct task, userland needs to know
what struct task looks like.

We need to consider having a pointer to a struct task here instead and
forward declare struct task in the !_KERNEL case.

Defer the vrele() on a jail's root vnode reference from prison_free()
to a new prison_complete() task run by a task queue. This removes
a requirement for grabbing Giant in crfree(). Embed the 'struct task'
in 'struct prison' so that we don't have to allocate memory from
prison_free() (which means we also defer the FREE()).

With this change, I believe grabbing Giant from crfree() can now be
removed, but need to check the uidinfo code paths.

To avoid header pollution, move the definition of 'struct task'
to _task.h, and recursively include from taskqueue.h and jail.h; much
preferably to all files including jail.h picking up a requirement to
include taskqueue.h.

Bumped into by: sam
Reviewed by: bde, tjr