[PATCH v2 07/10] libmultipath: handle TUR threads that can't be cancelled

[Martin Wilck <mwilck@suse.com>]

When the tur checker code determines that a hanging TUR thread
couldn't be cancelled, rather than simply returning, reallocate
the checker context and start a new thread. This will leak some
memory if the hanging thread never wakes up again, but well, in
that highly unlikely case we're leaking threads anyway.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 libmultipath/checkers/tur.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/libmultipath/checkers/tur.c b/libmultipath/checkers/tur.c
index 41210892..a6c88eb2 100644
--- a/libmultipath/checkers/tur.c
+++ b/libmultipath/checkers/tur.c
@@ -349,11 +349,29 @@ int libcheck_check(struct checker * c)
 		}
 	} else {
 		if (uatomic_read(&ct->holders) > 1) {
-			/* The thread has been cancelled but hasn't
-			 * quit. exit with timeout. */
+			/*
+			 * The thread has been cancelled but hasn't quit.
+			 * We have to prevent it from interfering with the new
+			 * thread. We create a new context and leave the old
+			 * one with the stale thread, hoping it will clean up
+			 * eventually.
+			 */
 			condlog(3, "%d:%d : tur thread not responding",
 				major(ct->devt), minor(ct->devt));
-			return PATH_TIMEOUT;
+
+			/*
+			 * libcheck_init will replace c->context.
+			 * It fails only in OOM situations. In this case, return
+			 * PATH_UNCHECKED to avoid prematurely failing the path.
+			 */
+			if (libcheck_init(c) != 0)
+				return PATH_UNCHECKED;
+
+			if (!uatomic_sub_return(&ct->holders, 1))
+				/* It did terminate, eventually */
+				cleanup_context(ct);
+
+			ct = c->context;
 		}
 		/* Start new TUR checker */
 		pthread_mutex_lock(&ct->lock);
-- 
2.19.1