From: Christoph Hellwig <[email protected]> [ Upstream commit 499cbe0f2fb0641cf07a1a8ac9f7317674295fea ]
Mark dm error as DM_TARGET_PASSES_INTEGRITY so that it can be stacked on top of PI capable devices. The claim is strictly speaking as lie as dm error fails all I/O and doesn't pass anything on, but doing the same for integrity I/O work just fine :) This helps to make about two dozen xfstests test cases pass on PI capable devices. Signed-off-by: Christoph Hellwig <[email protected]> Signed-off-by: Mikulas Patocka <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- LLM Generated explanations, may be completely bogus: YES - What changes: The patch adds `DM_TARGET_PASSES_INTEGRITY` to the error target’s feature bits, so the `error` target advertises that it “passes integrity” (even though it kills all I/O). In the upstream diff this is the sole functional change: `drivers/md/dm-target.c` updates `.features` to include `DM_TARGET_PASSES_INTEGRITY` alongside existing flags. - Upstream change site: drivers/md/dm-target.c (error target `.features` line). - In stable trees like v5.4, the analogous site is `drivers/md/dm- target.c:150`, where `.features = DM_TARGET_WILDCARD` currently lacks the integrity pass-through bit. - Why it matters: Device-mapper only allows integrity-enabled I/O to be cloned/mapped through a target if it either implements integrity itself or passes integrity through: - Clone-path gate: drivers/md/dm.c:1369–1376. If a bio has integrity and the target does not have `DM_TARGET_INTEGRITY` or `DM_TARGET_PASSES_INTEGRITY`, `clone_bio()` returns `-EIO`, failing the I/O. - Table registration gate: drivers/md/dm-table.c:1207 requires all targets in the table to pass integrity for the DM device to register an integrity profile; otherwise integrity stacking is disabled for the mapped device. - As a result, today stacking `dm-error` atop a PI-capable device can fail or silently disable integrity, which breaks real workloads and, as the commit notes, about two dozen xfstests on PI devices. - Correctness and safety: Marking the `error` target as “passes integrity” unblocks the two integrity gates above without changing the target’s behavior for data: - `io_err_map()` still returns `DM_MAPIO_KILL` (drivers/md/dm- target.c), so the request never reaches lower devices. - When integrity is present, the DM core will clone the integrity payload (drivers/md/dm.c:1369–1398) and then, because the target kills the I/O, `free_tio()` will `bio_put()` the clone, freeing the integrity payload (drivers/md/dm.c:633–647). No leaks, no functional change in outcomes (I/O still fails with error), only removal of spurious integrity gating. - Other simple pass-through targets already set this flag (e.g., `dm- linear`, `dm-mpath`, `dm-stripe`, `dm-delay`): drivers/md/dm- linear.c:220, drivers/md/dm-mpath.c:2009, drivers/md/dm- stripe.c:490, drivers/md/dm-delay.c:362. Aligning `dm-error` improves consistency. - Scope and risk: - Minimal, single-bit feature change, confined to the `dm-error` target. - No architectural changes; no user-visible behavior change except allowing integrity-enabled stacking where it previously errored or disabled integrity. - Security neutral; performance impact negligible (a short-lived integrity clone that is immediately freed on kill). - Backport notes: - The feature bit `DM_TARGET_PASSES_INTEGRITY` exists in stable series (include/linux/device-mapper.h:241–242), and the `error` target currently lacks it (drivers/md/dm-target.c:150 in v5.4). - Upstream diff also shows a `.version` bump and additional callbacks in newer kernels; for stable backports you can keep the version as- is and only add the feature bit. The functional fix is just the feature addition. - No dependencies on other recent changes. Given it fixes real failures with PI-capable devices, is tiny and self- contained, and aligns `dm-error` with other DM targets’ integrity behavior, this is a good candidate for stable backport. drivers/md/dm-target.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c index 2af5a9514c05e..8fede41adec00 100644 --- a/drivers/md/dm-target.c +++ b/drivers/md/dm-target.c @@ -263,7 +263,8 @@ static long io_err_dax_direct_access(struct dm_target *ti, pgoff_t pgoff, static struct target_type error_target = { .name = "error", .version = {1, 7, 0}, - .features = DM_TARGET_WILDCARD | DM_TARGET_ZONED_HM, + .features = DM_TARGET_WILDCARD | DM_TARGET_ZONED_HM | + DM_TARGET_PASSES_INTEGRITY, .ctr = io_err_ctr, .dtr = io_err_dtr, .map = io_err_map, -- 2.51.0
