On Wed, Jul 12, 2017 at 01:05:10PM -0700, Adam Buchbinder wrote:
> 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@xxxxxxxxxx>
Applied, thanks.
> ---
> image/main.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/image/main.c b/image/main.c
> index 1eca414..a5d01d8 100644
> --- a/image/main.c
> +++ b/image/main.c
> @@ -1715,14 +1715,15 @@ static void *restore_worker(void *data)
> }
> async = list_entry(mdres->list.next, struct async_work, list);
> list_del_init(&async->list);
> - pthread_mutex_unlock(&mdres->mutex);
>
> if (mdres->compress_method == COMPRESS_ZLIB) {
> size = compress_size;
> + pthread_mutex_unlock(&mdres->mutex);
> ret = uncompress(buffer, (unsigned long *)&size,
> async->buffer, async->bufsize);
> + pthread_mutex_lock(&mdres->mutex);
> if (ret != Z_OK) {
> - error("decompressiion failed with %d", ret);
> + error("decompression failed with %d", ret);
The typo fixes belong to a separate patch, as they fix a different
problem. We stick to the same style as in kernel "one patch per logical
change", so I'll split them to another patch as it's fairly trivial.
> err = -EIO;
> }
> outbuf = buffer;
> @@ -1798,7 +1799,6 @@ error:
> if (!mdres->multi_devices && async->start == BTRFS_SUPER_INFO_OFFSET)
> write_backup_supers(outfd, outbuf);
>
> - pthread_mutex_lock(&mdres->mutex);
> if (err && !mdres->error)
> mdres->error = err;
> mdres->num_items--;
> @@ -1899,7 +1899,7 @@ static int fill_mdres_info(struct mdrestore_struct *mdres,
> ret = uncompress(buffer, (unsigned long *)&size,
> async->buffer, async->bufsize);
> if (ret != Z_OK) {
> - error("decompressiion failed with %d", ret);
> + error("decompression failed with %d", ret);
> free(buffer);
> return -EIO;
> }
> @@ -1928,7 +1928,9 @@ static int add_cluster(struct meta_cluster *cluster,
> u32 i, nritems;
> int ret;
>
> + pthread_mutex_lock(&mdres->mutex);
> mdres->compress_method = header->compress;
> + pthread_mutex_unlock(&mdres->mutex);
>
> bytenr = le64_to_cpu(header->bytenr) + BLOCK_SIZE;
> nritems = le32_to_cpu(header->nritems);
> @@ -2171,7 +2173,7 @@ static int search_for_chunk_blocks(struct mdrestore_struct *mdres,
> continue;
> }
> error(
> - "unknown state after reading cluster at %llu, probably crrupted data",
> + "unknown state after reading cluster at %llu, probably corrupted data",
> cluster_bytenr);
> ret = -EIO;
> break;
> @@ -2220,7 +2222,7 @@ static int search_for_chunk_blocks(struct mdrestore_struct *mdres,
> (unsigned long *)&size, tmp,
> bufsize);
> if (ret != Z_OK) {
> - error("decompressiion failed with %d",
> + error("decompression failed with %d",
> ret);
> ret = -EIO;
> break;
> @@ -2340,7 +2342,7 @@ static int build_chunk_tree(struct mdrestore_struct *mdres,
> ret = uncompress(tmp, (unsigned long *)&size,
> buffer, le32_to_cpu(item->size));
> if (ret != Z_OK) {
> - error("decompressiion failed with %d", ret);
> + error("decompression failed with %d", ret);
> free(buffer);
> free(tmp);
> return -EIO;
> --
> 2.13.2.932.g7449e964c-goog
>
> --
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