Update deadman operation to better align with upstream OpenZFS

The deadman in ZoL didn't behave quite as it did in upstream
OpenZFS.  In addition to the 2 purposes for which OpenZFS used the
zfs_deadman_synctime_ms parameter, ZoL also used it to determine how
frequently the deadman would fire once it has been triggered.

This patch adds the zfs_deadman_checktime_ms parameter to control how
frequently the subsequent checks are performed.

The deadman is now disabled for suspended pools.

As had been the case, unlike upstream OpenZFS, ZoL will not panic when
a hung IO is detected.

The module parameter documentation has been upated to include the new
parameter and to better describe the operation of the deadmen.
    
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Closes #5695 

1 files changed, 26 insertions, 8 deletions

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index cca583de9..8b9a4e8cc 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -765,9 +765,28 @@ Default value: \fB0\fR.
 \fBzfs_deadman_enabled\fR (int)
 .ad
 .RS 12n
-Enable deadman timer. See description below.
+When a pool sync operation takes longer than \fBzfs_deadman_synctime_ms\fR
+milliseconds, a "slow spa_sync" message is logged to the debug log
+(see \fBzfs_dbgmsg_enable\fR).  If \fBzfs_deadman_enabled\fR is set,
+all pending IO operations are also checked and if any haven't completed
+within \fBzfs_deadman_synctime_ms\fR milliseconds, a "SLOW IO" message
+is logged to the debug log and a "delay" system event with the details of
+the hung IO is posted.
 .sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Use \fB1\fR (default) to enable the slow IO check and \fB0\fR to disable.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_checktime_ms\fR (int)
+.ad
+.RS 12n
+Once a pool sync operation has taken longer than
+\fBzfs_deadman_synctime_ms\fR milliseconds, continue to check for slow
+operations every \fBzfs_deadman_checktime_ms\fR milliseconds.
+.sp
+Default value: \fB5,000\fR.
 .RE
 
 .sp
@@ -776,12 +795,11 @@ Use \fB1\fR for yes (default) and \fB0\fR to disable.
 \fBzfs_deadman_synctime_ms\fR (ulong)
 .ad
 .RS 12n
-Expiration time in milliseconds. This value has two meanings. First it is
-used to determine when the spa_deadman() logic should fire. By default the
-spa_deadman() will fire if spa_sync() has not completed in 1000 seconds.
-Secondly, the value determines if an I/O is considered "hung". Any I/O that
-has not completed in zfs_deadman_synctime_ms is considered "hung" resulting
-in a zevent being logged.
+Interval in milliseconds after which the deadman is triggered and also
+the interval after which an IO operation is considered to be "hung"
+if \fBzfs_deadman_enabled\fR is set.
+
+See \fBzfs_deadman_enabled\fR.
 .sp
 Default value: \fB1,000,000\fR.
 .RE