Illumos #3552

3552 condensing one space map burns 3 seconds of CPU in spa_sync()
     thread (fix race condition)

References:
  https://www.illumos.org/issues/3552
  illumos/illumos-gate@03f8c366886542ed249a15d755ae78ea4e775d9d

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting notes:

This fixes an upstream regression that was introduced in commit
zfsonlinux/zfs@e51be06697762215dc3b679f8668987034a5a048, which
ported the Illumos 3552 changes. This fix was added to upstream
rather quickly, but at the time of the port, no one spotted it and
the race was rare enough that it passed our regression tests. I
discovered this when comparing our metaslab.c to the illumos
metaslab.c.

Without this change it is possible for metaslab_group_alloc() to
consume a large amount of cpu time.  Since this occurs under a
mutex in a rcu critical section the kernel will log this to the
console as a self-detected cpu stall as follows:

  INFO: rcu_sched self-detected stall on CPU { 0}
  (t=60000 jiffies g=11431890 c=11431889 q=18271)

Closes #1687
Closes #1720
Closes #1731
Closes #1747
Add missing dsl pool configuration lock

The semantics introduced by the restructured sync task of illumos
3464 require this lock when calling dmu_snapshot_list_next().
The pool is locked/unlocked for each iteration to reduce the
chance of long-running locks.

This was accidentally missed when doing the original port because
ZoL's control directory code is Linux-specific and is in a
different file than in illumos.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1785
Dedup-related documentation additions for zpool and zdb.

Document the "-D" and "-T" options and the optional interval
and count or "zpool status".

Also for zpool's man page, use a consistent order for the
various "-T" options to match the program's help output.

Document the effect of additional "-D" options for zdb.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1786
Linux 3.11 compat: Rename LZ4 symbols

Linus Torvalds merged LZ4 into Linux 3.11. This causes a conflict
whenever CONFIG_LZ4_DECOMPRESS=y or CONFIG_LZ4_COMPRESS=y are set in the
kernel's .config. We rename the symbols to avoid the conflict.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1789
Increase default udev wait time

When creating a new pool, or adding/replacing a disk in an existing
pool, partition tables will be automatically created on the devices.
Under normal circumstances it will take less than a second for udev
to create the expected device files under /dev/.  However, it has
been observed that if the system is doing heavy IO concurrently udev
may take far longer.  If you also throw in some cheap dodgy hardware
it may take even longer.

To prevent zpool commands from failing due to this the default wait
time for udev is being increased to 30 seconds.  This will have no
impact on normal usage, the increase timeout should only be noticed
if your udev rules are incorrectly configured.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1646