From 4257184a0fd276af7e1741dda8a7468a30b4a9c6 Mon Sep 17 00:00:00 2001
From: Tom Clegg <tom@tomclegg.ca>
Date: Wed, 11 Dec 2019 10:40:01 -0500
Subject: [PATCH] 15928: Fix deadlock.

Locking the parent dir isn't necessary to finish async writes, and
deadlocks if a waitPrune() is waiting for the async writes to finish.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@tomclegg.ca>
---
 sdk/go/arvados/fs_collection.go | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/sdk/go/arvados/fs_collection.go b/sdk/go/arvados/fs_collection.go
index 3d0928b84e..d0e97f2ad1 100644
--- a/sdk/go/arvados/fs_collection.go
+++ b/sdk/go/arvados/fs_collection.go
@@ -698,21 +698,9 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
 	go func() {
 		defer close(done)
 		defer close(errs)
-		locked := map[*filenode]bool{}
 		locator, _, err := dn.fs.PutB(block)
 		dn.fs.throttle().Release()
 		{
-			if !sync {
-				dn.Lock()
-				defer dn.Unlock()
-				for _, name := range dn.sortedNames() {
-					if fn, ok := dn.inodes[name].(*filenode); ok {
-						fn.Lock()
-						defer fn.Unlock()
-						locked[fn] = true
-					}
-				}
-			}
 			defer func() {
 				for _, seg := range segs {
 					if seg.flushing == done {
@@ -727,6 +715,7 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
 		}
 		for idx, ref := range refs {
 			if !sync {
+				ref.fn.Lock()
 				// In async mode, fn's lock was
 				// released while we were waiting for
 				// PutB(); lots of things might have
@@ -735,17 +724,15 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
 					// file segments have
 					// rearranged or changed in
 					// some way
+					ref.fn.Unlock()
 					continue
 				} else if seg, ok := ref.fn.segments[ref.idx].(*memSegment); !ok || seg != segs[idx] {
 					// segment has been replaced
+					ref.fn.Unlock()
 					continue
 				} else if seg.flushing != done {
 					// seg.buf has been replaced
-					continue
-				} else if !locked[ref.fn] {
-					// file was renamed, moved, or
-					// deleted since we called
-					// PutB
+					ref.fn.Unlock()
 					continue
 				}
 			}
@@ -763,6 +750,9 @@ func (dn *dirnode) commitBlock(ctx context.Context, refs []fnSegmentRef, bufsize
 			// lock, writing different segments from the
 			// same file.
 			atomic.AddInt64(&ref.fn.memsize, -int64(len(data)))
+			if !sync {
+				ref.fn.Unlock()
+			}
 		}
 	}()
 	if sync {
-- 
2.30.2