[PATCH 09/10] repair: fix prefetch queue limiting

[Dave Chinner]

From: Dave Chinner <dchinner at redhat.com>

The length of the prefetch queue is limited by a semaphore. To avoid
a ABBA deadlock, we only trywait on the semaphore so if we fail to
get it we can kick the IO queues before sleeping. Unfortunately,
the "need to sleep" detection is just a little wrong - it needs to
lok at errno, not err for the EAGAIN value.

Hence this queue throttling has not been working for a long time.

Signed-off-by: Dave Chinner <dchinner at redhat.com>
---
 repair/phase6.c   | 9 ++++++++-
 repair/prefetch.c | 2 +-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/repair/phase6.c b/repair/phase6.c
index c8bfa09..ff16120 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -2999,8 +2999,15 @@ traverse_function(
 		if (irec->ino_isa_dir == 0)
 			continue;
 
-		if (pf_args)
+		if (pf_args) {
 			sem_post(&pf_args->ra_count);
+#ifdef XR_PF_TRACE
+			sem_getvalue(&pf_args->ra_count, &i);
+			pftrace(
+		"processing inode chunk %p in AG %d (sem count = %d)",
+				irec, agno, i);
+#endif
+		}
 
 		for (i = 0; i < XFS_INODES_PER_CHUNK; i++)  {
 			if (inode_isadir(irec, i))
diff --git a/repair/prefetch.c b/repair/prefetch.c
index 7135d67..5158863 100644
--- a/repair/prefetch.c
+++ b/repair/prefetch.c
@@ -723,7 +723,7 @@ pf_queuing_worker(
 			irec, args->agno, i);
 #endif
 		err = sem_trywait(&args->ra_count);
-		if (err == EAGAIN) {
+		if (err < 0 && errno == EAGAIN) {
 			/*
 			 * Kick the queue once we have reached the limit;
 			 * without this the threads processing the inodes
-- 
1.8.4.rc3