dm: allocate a special workqueue for deferred device removal

The commit 2c140a246dc ("dm: allow remove to be deferred") introduced a
deferred removal feature for the device mapper.  When this feature is
used (by passing a flag DM_DEFERRED_REMOVE to DM_DEV_REMOVE_CMD ioctl)
and the user tries to remove a device that is currently in use, the
device will be removed automatically in the future when the last user
closes it.

Device mapper used the system workqueue to perform deferred removals.
However, some targets (dm-raid1, dm-mpath, dm-stripe) flush work items
scheduled for the system workqueue from their destructor.  If the
destructor itself is called from the system workqueue during deferred
removal, it introduces a possible deadlock - the workqueue tries to flush
itself.

Fix this possible deadlock by introducing a new workqueue for deferred
removals.  We allocate just one workqueue for all dm targets.  The
ability of dm targets to process IOs isn't dependent on deferred removal
of unused targets, so a deadlock due to shared workqueue isn't possible.

Also, cleanup local_init() to eliminate potential for returning success
on failure.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 3.13+
dm crypt, dm zero: update author name following legal name change

Signed-off-by: Jana Saout <jana@saout.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
dm io: fix a race condition in the wake up code for sync_io

There's a race condition between the atomic_dec_and_test(&io->count)
in dec_count() and the waking of the sync_io() thread.  If the thread
is spuriously woken immediately after the decrement it may exit,
making the on stack io struct invalid, yet the dec_count could still
be using it.

Fix this race by using a completion in sync_io() and dec_count().

Reported-by: Minfei Huang <huangminfei@ucloud.cn>
Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
dm mpath: fix IO hang due to logic bug in multipath_busy

Commit e80991773 ("dm mpath: push back requests instead of queueing")
modified multipath_busy() to return true if !pg_ready().  pg_ready()
checks the current state of the multipath device and may return false
even if a new IO is needed to change the state.

Bart Van Assche reported that he had multipath IO lockup when he was
performing cable pull tests.  Analysis showed that the multipath
device had a single path group with both paths active, but that the
path group itself was not active.  During the multipath device state
transitions 'queue_io' got set but nothing could clear it.  Clearing
'queue_io' only happens in __choose_pgpath(), but it won't be called
if multipath_busy() returns true due to pg_ready() returning false
when 'queue_io' is set.

As such the !pg_ready() check in multipath_busy() is wrong because new
IO will not be sent to multipath target and the multipath state change
won't happen.  That results in multipath IO lockup.

The intent of multipath_busy() is to avoid unnecessary cycles of
dequeue + request_fn + requeue if it is known that the multipath
device will requeue.

Such "busy" situations would be:
  - path group is being activated
  - there is no path and the multipath is setup to requeue if no path

Fix multipath_busy() to return "busy" early only for these specific
situations.

Reported-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v3.15
powerpc/cell: Fix compilation with CONFIG_COREDUMP=n

Commit 046d662f4818 "coredump: make core dump functionality optional"
made the coredump optional, but didn't update the spufs code that
depends on it. That leads to build errors such as:

  arch/powerpc/platforms/built-in.o: In function `.spufs_arch_write_note':
  coredump.c:(.text+0x22cd4): undefined reference to `.dump_emit'
  coredump.c:(.text+0x22cf4): undefined reference to `.dump_emit'
  coredump.c:(.text+0x22d0c): undefined reference to `.dump_align'
  coredump.c:(.text+0x22d48): undefined reference to `.dump_emit'
  coredump.c:(.text+0x22e7c): undefined reference to `.dump_skip'

Fix it by adding some ifdefs in the cell code.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc: Clean up MMU_FTRS_A2 and MMU_FTR_TYPE_3E

In fb5a515704d7 "powerpc: Remove platforms/wsp and associated pieces",
we removed the last user of MMU_FTRS_A2. So remove it.

MMU_FTRS_A2 was the last user of MMU_FTR_TYPE_3E, so remove it also.
This leaves some unreachable code in mmu_context_nohash.c, so remove
that also.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc/powernv: Check for IRQHAPPENED before sleeping

Commit 8d6f7c5a: "powerpc/powernv: Make it possible to skip the IRQHAPPENED
check in power7_nap()" added code that prevents cpus from checking for
pending interrupts just before entering sleep state, which is wrong. These
interrupts are delivered during the soft irq disabled state of the cpu.

A cpu cannot enter any idle state with pending interrupts because they will
never be serviced until the next time the cpu is woken up by some other
interrupt. Its only then that the pending interrupts are replayed. This can result
in device timeouts or warnings about this cpu being stuck.

This patch fixes ths issue by ensuring that cpus check for pending interrupts
just before entering any idle state as long as they are not in the path of split
core operations.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc/kvm: Remove redundant save of SIER AND MMCR2

These two registers are already saved in the block above. Aside from
being unnecessary, by the time we get down to the second save location
r8 no longer contains MMCR2, so we are clobbering the saved value with
PMC5.

MMCR2 primarily consists of counter freeze bits. So restoring the value
of PMC5 into MMCR2 will most likely have the effect of freezing
counters.

Fixes: 72cde5a88d37 ("KVM: PPC: Book3S HV: Save/restore host PMU registers that are new in POWER8")
Cc: stable@vger.kernel.org
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc/perf: Add PPMU_ARCH_207S define

Instead of separate bits for every POWER8 PMU feature, have a single one
for v2.07 of the architecture.

This saves us adding a MMCR2 define for a future patch.

Cc: stable@vger.kernel.org
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc/perf: Clear MMCR2 when enabling PMU

On POWER8 when switching to a KVM guest we set bits in MMCR2 to freeze
the PMU counters. Aside from on boot they are then never reset,
resulting in stuck perf counters for any user in the guest or host.

We now set MMCR2 to 0 whenever enabling the PMU, which provides a sane
state for perf to use the PMU counters under either the guest or the
host.

This was manifesting as a bug with ppc64_cpu --frequency:

    $ sudo ppc64_cpu --frequency
    WARNING: couldn't run on cpu 0
    WARNING: couldn't run on cpu 8
      ...
    WARNING: couldn't run on cpu 144
    WARNING: couldn't run on cpu 152
    min:    18446744073.710 GHz (cpu -1)
    max:    0.000 GHz (cpu -1)
    avg:    0.000 GHz

The command uses a perf counter to measure CPU cycles over a fixed
amount of time, in order to approximate the frequency of the machine.
The counters were returning zero once a guest was started, regardless of
weather it was still running or had been shut down.

By dumping the value of MMCR2, it was observed that once a guest is
running MMCR2 is set to 1s - which stops counters from running:

    $ sudo sh -c 'echo p > /proc/sysrq-trigger'
    CPU: 0 PMU registers, ppmu = POWER8 n_counters = 6
    PMC1:  5b635e38 PMC2: 00000000 PMC3: 00000000 PMC4: 00000000
    PMC5:  1bf5a646 PMC6: 5793d378 PMC7: deadbeef PMC8: deadbeef
    MMCR0: 0000000080000000 MMCR1: 000000001e000000 MMCRA: 0000040000000000
    MMCR2: fffffffffffffc00 EBBHR: 0000000000000000
    EBBRR: 0000000000000000 BESCR: 0000000000000000
    SIAR:  00000000000a51cc SDAR:  c00000000fc40000 SIER:  0000000001000000

This is done unconditionally in book3s_hv_interrupts.S upon entering the
guest, and the original value is only save/restored if the host has
indicated it was using the PMU. This is okay, however the user of the
PMU needs to ensure that it is in a defined state when it starts using
it.

Fixes: e05b9b9e5c10 ("powerpc/perf: Power8 PMU support")
Cc: stable@vger.kernel.org
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc: Disable RELOCATABLE for COMPILE_TEST with PPC64

powerpc:allmodconfig has been failing for some time with the following
error.

arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
arch/powerpc/kernel/exceptions-64s.S:1312: Error: attempt to move .org backwards
make[1]: *** [arch/powerpc/kernel/head_64.o] Error 1

A number of attempts to fix the problem by moving around code have been
unsuccessful and resulted in failed builds for some configurations and
the discovery of toolchain bugs.

Fix the problem by disabling RELOCATABLE for COMPILE_TEST builds instead.
While this is less than perfect, it avoids substantial code changes
which would otherwise be necessary just to make COMPILE_TEST builds
happy and might have undesired side effects.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
powerpc/perf: Never program book3s PMCs with values >= 0x80000000

We are seeing a lot of PMU warnings on POWER8:

    Can't find PMC that caused IRQ

Looking closer, the active PMC is 0 at this point and we took a PMU
exception on the transition from negative to 0. Some versions of POWER8
have an issue where they edge detect and not level detect PMC overflows.

A number of places program the PMC with (0x80000000 - period_left),
where period_left can be negative. We can either fix all of these or
just ensure that period_left is always >= 1.

This patch takes the second option.

Cc: <stable@vger.kernel.org>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Merge branch 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc

Pull powerpc fixes from Ben Herrenschmidt:
 "Here are a few more powerpc fixes for 3.16

  There's a small series of 3 patches that fix saving/restoring MMUCR2
  when using KVM without which perf goes completely bonkers in the host
  system.  Another perf fix from Anton that's been rotting away in
  patchwork due to my poor eyesight, a couple of compile fixes, a little
  addition to the WSP removal by Michael (removing a bit more dead
  stuff) and a fix for an embarassing regression with our soft irq
  masking"

* 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc:
  powerpc/perf: Never program book3s PMCs with values >= 0x80000000
  powerpc: Disable RELOCATABLE for COMPILE_TEST with PPC64
  powerpc/perf: Clear MMCR2 when enabling PMU
  powerpc/perf: Add PPMU_ARCH_207S define
  powerpc/kvm: Remove redundant save of SIER AND MMCR2
  powerpc/powernv: Check for IRQHAPPENED before sleeping
  powerpc: Clean up MMU_FTRS_A2 and MMU_FTR_TYPE_3E
  powerpc/cell: Fix compilation with CONFIG_COREDUMP=n
Merge tag 'dm-3.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper fixes from Mike Snitzer:

 - Fix DM multipath IO hang regression from 3.15 due to logic bug in
   multipath_busy.  This impacted cable-pull testing and also the
   ability to boot with IPR SCSI on a POWER8 box.

 - Fix possible deadlock with deferred device removal by using a new
   dedicated workqueue rather than using the system workqueue.

 - Fix NULL pointer crash due to race condition in dm-io's wake up code
   for sync_io by using a completion.

 - Update dm-crypt and dm-zero author name following legal name change;
   this is important to Jana so I didn't see any reason to hold it back.

* tag 'dm-3.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm mpath: fix IO hang due to logic bug in multipath_busy
  dm io: fix a race condition in the wake up code for sync_io
  dm crypt, dm zero: update author name following legal name change
  dm: allocate a special workqueue for deferred device removal