6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Qu Wenruo <wqu@xxxxxxxx>
[ 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-uninitialized]]
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@xxxxxxxxxx/
Fixes: ae76d8e3e135 ("btrfs: scrub: fix grouping of read IO")
Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 */
--
2.42.0
