Mesa (staging/21.2): util/fossilize_db: Be conservative about header length check for locking.

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Module: Mesa
Branch: staging/21.2
Commit: 8441124d0bdc75ebcbc7cd3504f4a29d6549ed34
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=8441124d0bdc75ebcbc7cd3504f4a29d6549ed34

Author: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Date:   Thu Aug  5 01:30:25 2021 +0200

util/fossilize_db: Be conservative about header length check for locking.

Don't anticipate seeing any partial written headers but just in case we
should probably wait on the lock to make sure whatever header was being
written is finished being written.

Fixes: 4f0f8133a35 "util/fossilize_db: Do not lock the fossilize db permanently."
Reviewed-by: Timothy Arceri <tarceri at itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12204>
(cherry picked from commit 96bfefe8d1209b6aaa56fd77ca570789d82efb6e)

---

 .pick_status.json       | 2 +-
 src/util/fossilize_db.c | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index 67a0e9ac367..7dd7ae31470 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -598,7 +598,7 @@
         "description": "util/fossilize_db: Be conservative about header length check for locking.",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "4f0f8133a35ec2fec8d99936cd7425e40d092169"
     },
diff --git a/src/util/fossilize_db.c b/src/util/fossilize_db.c
index af5c6e58581..46217f8a597 100644
--- a/src/util/fossilize_db.c
+++ b/src/util/fossilize_db.c
@@ -203,8 +203,9 @@ load_foz_dbs(struct foz_db *foz_db, FILE *db_idx, uint8_t file_idx,
    size_t len = ftell(db_idx);
    rewind(db_idx);
 
-   /* Try not to take the lock if len > 0, but if it is 0 we take the lock to initialize the files. */
-   if (len == 0) {
+   /* Try not to take the lock if len >= the size of the header, but if it is smaller we take the
+    * lock to potentially initialize the files. */
+   if (len < sizeof(stream_reference_magic_and_version)) {
       /* Wait for 100 ms in case of contention, after that we prioritize getting the app started. */
       int err = lock_file_with_timeout(foz_db->file[file_idx], 100000000);
       if (err == -1)