From d9dfe299a44f1a77ad027a8fdc9a2340c2de1dd1 Mon Sep 17 00:00:00 2001
From: Josh Hawkins <32435876+hawkeye217@users.noreply.github.com>
Date: Fri, 22 May 2026 08:46:17 -0500
Subject: [PATCH] drop stale shm cache refs when cached segment size doesn't
 match requested shape
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The cached SharedMemoryFrameManager reference can point at a segment whose
size no longer matches the requested shape — the segment was unlinked and
recreated at a different size in a camera add/remove cycle. This catches
both a resolution increase (cached too small) and a decrease (cached too
large, pointing at an orphaned inode whose stale bytes would otherwise be
misinterpreted at the new shape, producing distorted/miscolored YUV frames).

After reopening, if the OS-level segment still doesn't match the requested
shape we're in a transient mid-recreate state — either the maintainer
hasn't allocated the new segment yet (size too small) or we opened a
pre-recycle segment (size too big). Either way, skip the frame and don't
cache the mismatched ref.
---
 frigate/util/image.py | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/frigate/util/image.py b/frigate/util/image.py
index 4054c54182..d2832d97a0 100644
--- a/frigate/util/image.py
+++ b/frigate/util/image.py
@@ -1091,11 +1091,8 @@ class SharedMemoryFrameManager(FrameManager):
         try:
             required = int(np.prod(shape))
             shm = self.shm_store.get(name)
-            if shm is not None and shm.size < required:
-                # Cached reference points at an older, smaller segment
-                # that was unlinked and recreated at a larger size in a
-                # camera add/remove cycle. Drop the stale ref so we
-                # reopen the current segment.
+            if shm is not None and shm.size != required:
+                # stale cached ref from a same-name recreate — drop and reopen
                 try:
                     shm.close()
                 except Exception:
@@ -1104,12 +1101,8 @@ class SharedMemoryFrameManager(FrameManager):
                 shm = None
             if shm is None:
                 shm = UntrackedSharedMemory(name=name)
-                if shm.size < required:
-                    # Transient mid-recreate state: the OS-level segment
-                    # is still at the previous (smaller) size because the
-                    # maintainer hasn't allocated the new one yet. Don't
-                    # cache it (so the next call re-opens once the
-                    # maintainer has caught up) and skip this frame.
+                if shm.size != required:
+                    # mid-recreate: OS segment doesn't match shape yet; skip
                     try:
                         shm.close()
                     except Exception: