Kernel/Ext2FS: Uncache unknown inode indices when flushing writes

Ext2FS::get_inode() will remember unknown inode indices that it has
been asked about and put them into the inode cache as null inodes.

flush_writes() was not null-checking these while iterating, which
was a bug I finally managed to hit.

Flushing also seemed like a good time to drop unknown inodes from
the cache, since there's no good reason to hold to them indefinitely.

1 files changed, 7 insertions, 0 deletions

diff --git a/Kernel/FileSystem/Ext2FileSystem.cpp b/Kernel/FileSystem/Ext2FileSystem.cpp
index bd2b081129..ade39a1a8d 100644
--- a/Kernel/FileSystem/Ext2FileSystem.cpp
+++ b/Kernel/FileSystem/Ext2FileSystem.cpp
@@ -718,6 +718,13 @@ void Ext2FS::flush_writes()
     //        for their (child name lookup) and (block list) caches.
     Vector<InodeIndex> unused_inodes;
     for (auto& it : m_inode_cache) {
+        // NOTE: If we're asked to look up an inode by number (via get_inode) and it turns out
+        //       to not exist, we remember the fact that it doesn't exist by caching a nullptr.
+        //       This seems like a reasonable time to uncache ideas about unknown inodes, so do that.
+        if (!it.value) {
+            unused_inodes.append(it.key);
+            continue;
+        }
         if (it.value->ref_count() != 1)
             continue;
         if (it.value->has_watchers())