OpenZFS 9425 - channel programs can be interrupted

Problem Statement
=================
ZFS Channel program scripts currently require a timeout, so that hung or
long-running scripts return a timeout error instead of causing ZFS to get
wedged. This limit can currently be set up to 100 million Lua instructions.
Even with a limit in place, it would be desirable to have a sys admin
(support engineer) be able to cancel a script that is taking a long time.

Proposed Solution
=================
Make it possible to abort a channel program by sending an interrupt signal.In
the underlying txg_wait_sync function, switch the cv_wait to a cv_wait_sig to
catch the signal. Once a signal is encountered, the dsl_sync_task function can
install a Lua hook that will get called before the Lua interpreter executes a
new line of code. The dsl_sync_task can resume with a standard txg_wait_sync
call and wait for the txg to complete.  Meanwhile, the hook will abort the
script and indicate that the channel program was canceled. The kernel returns
a EINTR to indicate that the channel program run was canceled.

Porting notes: Added missing return value from cv_wait_sig()

Authored by: Don Brady <[email protected]>
Reviewed by: Sebastien Roy <[email protected]>
Reviewed by: Serapheim Dimitropoulos <[email protected]>
Reviewed by: Matt Ahrens <[email protected]>
Reviewed by: Sara Hartse <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Robert Mustacchi <[email protected]>
Ported-by: Don Brady <[email protected]>
Signed-off-by: Don Brady <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/9425
OpenZFS-commit: https://github.com/illumos/illumos-gate/commit/d0cb1fb926
Closes #8904 

1 files changed, 18 insertions, 1 deletions

diff --git a/module/spl/spl-condvar.c b/module/spl/spl-condvar.c
index a7a9d1db9..19c575f77 100644
--- a/module/spl/spl-condvar.c
+++ b/module/spl/spl-condvar.c
@@ -29,6 +29,12 @@
 #include <linux/hrtimer.h>
 #include <linux/compiler_compat.h>
 
+#include <linux/sched.h>
+
+#ifdef HAVE_SCHED_SIGNAL_HEADER
+#include <linux/sched/signal.h>
+#endif
+
 void
 __cv_init(kcondvar_t *cvp, char *name, kcv_type_t type, void *arg)
 {
@@ -144,10 +150,21 @@ __cv_wait_io(kcondvar_t *cvp, kmutex_t *mp)
 }
 EXPORT_SYMBOL(__cv_wait_io);
 
-void
+int
+__cv_wait_io_sig(kcondvar_t *cvp, kmutex_t *mp)
+{
+	cv_wait_common(cvp, mp, TASK_INTERRUPTIBLE, 1);
+
+	return (signal_pending(current) ? 0 : 1);
+}
+EXPORT_SYMBOL(__cv_wait_io_sig);
+
+int
 __cv_wait_sig(kcondvar_t *cvp, kmutex_t *mp)
 {
 	cv_wait_common(cvp, mp, TASK_INTERRUPTIBLE, 0);
+
+	return (signal_pending(current) ? 0 : 1);
 }
 EXPORT_SYMBOL(__cv_wait_sig);