From fb2abc538035e47fd1615ab6cf754a5d1bb3e70e Mon Sep 17 00:00:00 2001
From: Pavel Kalinnikov <pavel@cockroachlabs.com>
Date: Wed, 22 Nov 2023 17:26:44 +0000
Subject: [PATCH 1/3] pebble: fix deadlock after MemFS.SetIgnoreSyncs

Before this fix, if someone calls SetIgnoreSyncs() on a non-strict
MemFS, it does not unlock the mutex before returning. This causes all
other methods of MemFS to deadlock.
---
 vfs/mem_fs.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/vfs/mem_fs.go b/vfs/mem_fs.go
index 7ccd8e71d69..19f6fc61247 100644
--- a/vfs/mem_fs.go
+++ b/vfs/mem_fs.go
@@ -117,11 +117,11 @@ func (y *MemFS) String() string {
 // SetIgnoreSyncs sets the MemFS.ignoreSyncs field. See the usage comment with NewStrictMem() for
 // details.
 func (y *MemFS) SetIgnoreSyncs(ignoreSyncs bool) {
-	y.mu.Lock()
 	if !y.strict {
 		// noop
 		return
 	}
+	y.mu.Lock()
 	y.ignoreSyncs = ignoreSyncs
 	y.mu.Unlock()
 }

From 3c57d69b0788537f929c07aa2c748c7b92c24cde Mon Sep 17 00:00:00 2001
From: Pavel Kalinnikov <pavel@cockroachlabs.com>
Date: Wed, 22 Nov 2023 17:31:24 +0000
Subject: [PATCH 2/3] pebble: panic on incorrect strict MemFS methods use

Strict MemFS methods can be used by mistake on a non-strict MemFS. Panic
if this happens, instead of (previously) ignoring this silently. This
saves a test writer time being confused if they mis-use the type.
---
 vfs/mem_fs.go | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/vfs/mem_fs.go b/vfs/mem_fs.go
index 19f6fc61247..56cc4741319 100644
--- a/vfs/mem_fs.go
+++ b/vfs/mem_fs.go
@@ -118,8 +118,7 @@ func (y *MemFS) String() string {
 // details.
 func (y *MemFS) SetIgnoreSyncs(ignoreSyncs bool) {
 	if !y.strict {
-		// noop
-		return
+		panic("SetIgnoreSyncs can only be used on a strict MemFS")
 	}
 	y.mu.Lock()
 	y.ignoreSyncs = ignoreSyncs
@@ -130,8 +129,7 @@ func (y *MemFS) SetIgnoreSyncs(ignoreSyncs bool) {
 // NewStrictMem() for details.
 func (y *MemFS) ResetToSyncedState() {
 	if !y.strict {
-		// noop
-		return
+		panic("ResetToSyncedState can only be used on a strict MemFS")
 	}
 	y.mu.Lock()
 	y.root.resetToSyncedState()

From f5319e5c5c4b4d8ce094b535ec41f79b84695f70 Mon Sep 17 00:00:00 2001
From: Pavel Kalinnikov <pavel@cockroachlabs.com>
Date: Wed, 22 Nov 2023 17:35:13 +0000
Subject: [PATCH 3/3] pebble: unindent MemFS.Sync() while here

---
 vfs/mem_fs.go | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/vfs/mem_fs.go b/vfs/mem_fs.go
index 56cc4741319..fa44847b4f4 100644
--- a/vfs/mem_fs.go
+++ b/vfs/mem_fs.go
@@ -773,22 +773,23 @@ func (f *memFile) Stat() (os.FileInfo, error) {
 }
 
 func (f *memFile) Sync() error {
-	if f.fs != nil && f.fs.strict {
-		f.fs.mu.Lock()
-		defer f.fs.mu.Unlock()
-		if f.fs.ignoreSyncs {
-			return nil
-		}
-		if f.n.isDir {
-			f.n.syncedChildren = make(map[string]*memNode)
-			for k, v := range f.n.children {
-				f.n.syncedChildren[k] = v
-			}
-		} else {
-			f.n.mu.Lock()
-			f.n.mu.syncedData = slices.Clone(f.n.mu.data)
-			f.n.mu.Unlock()
+	if f.fs == nil || !f.fs.strict {
+		return nil
+	}
+	f.fs.mu.Lock()
+	defer f.fs.mu.Unlock()
+	if f.fs.ignoreSyncs {
+		return nil
+	}
+	if f.n.isDir {
+		f.n.syncedChildren = make(map[string]*memNode)
+		for k, v := range f.n.children {
+			f.n.syncedChildren[k] = v
 		}
+	} else {
+		f.n.mu.Lock()
+		f.n.mu.syncedData = slices.Clone(f.n.mu.data)
+		f.n.mu.Unlock()
 	}
 	return nil
 }