watchdog: Fix warning caused by use of smp_processor_id()

watchdog driver creates per-cpu kernel threads that are bound to
separate cpus. Use of smp_processor_id() by such threads in
__touch_watchdog() is perfectly fine, as they are generally pinned to
the cpu on which they are running.

During cpu offline event, however, affinity for the watchdog thread
bound to dying cpu is broken before it is killed. There is a small
time window between affinity broken and thread dying in which thread
can run on a cpu with its affinity not set to that cpu exclusively.
This will trigger a warning from use of smp_processor_id(), which is
harmless in this case as it will provide the required heartbeat on cpu
where it is running and moreover that thread will be shortly killed.

Mute the harmless warning by use of raw_smp_processor_id() in
__touch_watchdog(). This seems less intrusive fix than killing threads
in CPU_DOWN_PREPARE event handler.

Change-Id: I7fa22ff529aeea0ec3d5610cfec87aea92cf95a0
CRs-Fixed: 517188
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
ARM: smp: Save CPU registers before IPI_CPU_STOP processing

When a kernel panic occurs on one CPU, other CPUs are instructed to stop
execution via the IPI_CPU_STOP message. These other CPUs dump their stack,
which may not be good enough to reconstruct their context to perform
post-mortem analysis. Dump each CPU's context
(before it started procesing the IPI) into a globally accessible structure
to allow for easier post-mortem debugging.

Change-Id: I68ac75f73d7ddaebaff9122b23e341bcb00e8fb9
Signed-off-by: Tingting Yang <tingting@codeaurora.org>
sync: don't block the flusher thread waiting on IO

When sync does it's WB_SYNC_ALL writeback, it issues data Io and
then immediately waits for IO completion. This is done in the
context of the flusher thread, and hence completely ties up the
flusher thread for the backing device until all the dirty inodes
have been synced. On filesystems that are dirtying inodes constantly
and quickly, this means the flusher thread can be tied up for
minutes per sync call and hence badly affect system level write IO
performance as the page cache cannot be cleaned quickly.

We already have a wait loop for IO completion for sync(2), so cut
this out of the flusher thread and delegate it to wait_sb_inodes().
Hence we can do rapid IO submission, and then wait for it all to
complete.

Effect of sync on fsmark before the patch:

FSUse%        Count         Size    Files/sec     App Overhead
.....
     0       640000         4096      35154.6          1026984
     0       720000         4096      36740.3          1023844
     0       800000         4096      36184.6           916599
     0       880000         4096       1282.7          1054367
     0       960000         4096       3951.3           918773
     0      1040000         4096      40646.2           996448
     0      1120000         4096      43610.1           895647
     0      1200000         4096      40333.1           921048

And a single sync pass took:

  real    0m52.407s
  user    0m0.000s
  sys     0m0.090s

After the patch, there is no impact on fsmark results, and each
individual sync(2) operation run concurrently with the same fsmark
workload takes roughly 7s:

  real    0m6.930s
  user    0m0.000s
  sys     0m0.039s

IOWs, sync is 7-8x faster on a busy filesystem and does not have an
adverse impact on ongoing async data write operations.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>