This reverts commit 616c310e83b872024271c915c1b9ab505b9efad9.
(Move PREEMPT_RCU preemption to switch_to() invocation).
Testing by Sasha Levin <levinsasha928@gmail.com> showed that this
can result in deadlock due to invoking the scheduler when one of
the runqueue locks is held.  Because this commit was simply a
performance optimization, revert it.

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Sasha Levin <levinsasha928@gmail.com>

Pull UML updates from Richard Weinberger:
 "Most changes are bug fixes and cleanups"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml:
  um: missing checks of __put_user()/__get_user() return values
  um: stub_rt_sigsuspend isn't needed these days anymore
  um/x86: merge (and trim) 32- and 64-bit variants of ptrace.h
  irq: Remove irq_chip->release()
  um: Remove CONFIG_IRQ_RELEASE_METHOD
  um: Remove usage of irq_chip->release()
  um: Implement um_free_irq()
  um: Fix __swp_type()
  um: Implement a custom pte_same() function
  um: Add BUG() to do_ops()'s error path
  um: Remove unused variables
  um: bury unused _TIF_RESTORE_SIGMASK
  um: wrong sigmask saved in case of multiple sigframes
  um: add TIF_NOTIFY_RESUME
  um: ->restart_block.fn needs to be reset on sigreturn

Instead of using chip->release() we can achieve the same
using a simple wrapper for free_irq().
We have already um_request_irq(), so um_free_irq() is the perfect
counterpart.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Currently, PREEMPT_RCU readers are enqueued upon entry to the scheduler.
This is inefficient because enqueuing is required only if there is a
context switch, and entry to the scheduler does not guarantee a context
switch.

The commit therefore moves the enqueuing to immediately precede the
call to switch_to() from the scheduler.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Richard Weinberger <richard@nod.at>
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
CC: dhowells@redhat.com

... rather than open-coding the 64bit versions.  endian.h has those guys.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

Pull UML changes from Richard Weinberger:
 "Mostly bug fixes and cleanups"

* 'for-linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml: (35 commits)
  um: Update defconfig
  um: Switch to large mcmodel on x86_64
  MTD: Relax dependencies
  um: Wire CONFIG_GENERIC_IO up
  um: Serve io_remap_pfn_range()
  Introduce CONFIG_GENERIC_IO
  um: allow SUBARCH=x86
  um: most of the SUBARCH uses can be killed
  um: deadlock in line_write_interrupt()
  um: don't bother trying to rebuild CHECKFLAGS for USER_OBJS
  um: use the right ifdef around exports in user_syms.c
  um: a bunch of headers can be killed by using generic-y
  um: ptrace-generic.h doesn't need user.h
  um: kill HOST_TASK_PID
  um: remove pointless include of asm/fixmap.h from asm/pgtable.h
  um: asm-offsets.h might as well come from underlying arch...
  um: merge processor_{32,64}.h a bit...
  um: switch close_chan() to struct line
  um: race fix: initialize delayed_work *before* registering IRQ
  um: line->have_irq is never checked...
  ...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

... and switch chan_interrupt() to directly calling close_one_chan(),
so we can lose delay_free_irq argument of close_chan() as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

... since chan_interrupt() might schedule it if there's too much
incoming data.  Kill task argument of chan_interrupt(), while
we are at it - it's always &line->task.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>