6.6-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
[ Upstream commit 47e2b06b7b5cb356a987ba3429550c3a89ea89d6 ]
[BUG] There is a compilation warning reported on commit ae76d8e3e135 ("btrfs: scrub: fix grouping of read IO"), where gcc (14.0.0 20231022 experimental) is reporting the following uninitialized variable:
fs/btrfs/scrub.c: In function ‘scrub_simple_mirror.isra’: fs/btrfs/scrub.c:2075:29: error: ‘found_logical’ may be used uninitialized [-Werror=maybe-uninitialized[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmaybe-uniniti...]] 2075 | cur_logical = found_logical + BTRFS_STRIPE_LEN; fs/btrfs/scrub.c:2040:21: note: ‘found_logical’ was declared here 2040 | u64 found_logical; | ^~~~~~~~~~~~~
[CAUSE] This is a false alert, as @found_logical is passed as parameter @found_logical_ret of function queue_scrub_stripe().
As long as queue_scrub_stripe() returned 0, we would update @found_logical_ret. And if queue_scrub_stripe() returned >0 or <0, the caller would not utilized @found_logical, thus there should be nothing wrong.
Although the triggering gcc is still experimental, it looks like the extra check on "if (found_logical_ret)" can sometimes confuse the compiler.
Meanwhile the only caller of queue_scrub_stripe() is always passing a valid pointer, there is no need for such check at all.
[FIX] Although the report itself is a false alert, we can still make it more explicit by:
- Replace the check for @found_logical_ret with ASSERT()
- Initialize @found_logical to U64_MAX
- Add one extra ASSERT() to make sure @found_logical got updated
Link: https://lore.kernel.org/linux-btrfs/87fs1x1p93.fsf@gentoo.org/ Fixes: ae76d8e3e135 ("btrfs: scrub: fix grouping of read IO") Reviewed-by: Anand Jain anand.jain@oracle.com Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/scrub.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index b877203f1dc5a..4445a52a07076 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -1798,6 +1798,9 @@ static int queue_scrub_stripe(struct scrub_ctx *sctx, struct btrfs_block_group * */ ASSERT(sctx->cur_stripe < SCRUB_TOTAL_STRIPES);
+ /* @found_logical_ret must be specified. */ + ASSERT(found_logical_ret); + stripe = &sctx->stripes[sctx->cur_stripe]; scrub_reset_stripe(stripe); ret = scrub_find_fill_first_stripe(bg, &sctx->extent_path, @@ -1806,8 +1809,7 @@ static int queue_scrub_stripe(struct scrub_ctx *sctx, struct btrfs_block_group * /* Either >0 as no more extents or <0 for error. */ if (ret) return ret; - if (found_logical_ret) - *found_logical_ret = stripe->logical; + *found_logical_ret = stripe->logical; sctx->cur_stripe++;
/* We filled one group, submit it. */ @@ -2010,7 +2012,7 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
/* Go through each extent items inside the logical range */ while (cur_logical < logical_end) { - u64 found_logical; + u64 found_logical = U64_MAX; u64 cur_physical = physical + cur_logical - logical_start;
/* Canceled? */ @@ -2045,6 +2047,8 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx, if (ret < 0) break;
+ /* queue_scrub_stripe() returned 0, @found_logical must be updated. */ + ASSERT(found_logical != U64_MAX); cur_logical = found_logical + BTRFS_STRIPE_LEN;
/* Don't hold CPU for too long time */