btrfs-progs: image: Fix data races when reporting progress
Making the code data-race safe requires that reads *and* writes happen under a mutex lock, if any of the access are writes. See Dmitri Vyukov, "Benign data races: what could possibly go wrong?" for more details. The fix here was to put most of the main loop of restore_worker under a mutex lock. This race was detected using fsck-tests/012-leaf-corruption. ================== WARNING: ThreadSanitizer: data race Write of size 4 by main thread: #0 add_cluster btrfs-progs/image/main.c:1931 #1 restore_metadump btrfs-progs/image/main.c:2566 #2 main btrfs-progs/image/main.c:2859 Previous read of size 4 by thread T6: #0 restore_worker btrfs-progs/image/main.c:1720 Location is stack of main thread. Thread T6 (running) created by main thread at: #0 pthread_create <null> #1 mdrestore_init btrfs-progs/image/main.c:1868 #2 restore_metadump btrfs-progs/image/main.c:2534 #3 main btrfs-progs/image/main.c:2859 SUMMARY: ThreadSanitizer: data race btrfs-progs/image/main.c:1931 in add_cluster Signed-off-by: Adam Buchbinder <abuchbinder@google.com> Signed-off-by: David Sterba <dsterba@suse.com>
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@ -1720,12 +1720,13 @@ static void *restore_worker(void *data)
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}
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async = list_entry(mdres->list.next, struct async_work, list);
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list_del_init(&async->list);
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pthread_mutex_unlock(&mdres->mutex);
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if (mdres->compress_method == COMPRESS_ZLIB) {
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size = compress_size;
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pthread_mutex_unlock(&mdres->mutex);
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ret = uncompress(buffer, (unsigned long *)&size,
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async->buffer, async->bufsize);
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pthread_mutex_lock(&mdres->mutex);
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if (ret != Z_OK) {
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error("decompressiion failed with %d", ret);
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err = -EIO;
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@ -1803,7 +1804,6 @@ error:
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if (!mdres->multi_devices && async->start == BTRFS_SUPER_INFO_OFFSET)
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write_backup_supers(outfd, outbuf);
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pthread_mutex_lock(&mdres->mutex);
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if (err && !mdres->error)
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mdres->error = err;
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mdres->num_items--;
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@ -1933,7 +1933,9 @@ static int add_cluster(struct meta_cluster *cluster,
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u32 i, nritems;
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int ret;
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pthread_mutex_lock(&mdres->mutex);
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mdres->compress_method = header->compress;
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pthread_mutex_unlock(&mdres->mutex);
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bytenr = le64_to_cpu(header->bytenr) + BLOCK_SIZE;
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nritems = le32_to_cpu(header->nritems);
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