[PATCH AUTOSEL 6.18-6.12] scsi: devinfo: Add BLIST_SKIP_IO_HINTS for EMC Symmetrix
From: Sasha Levin
Date: Mon Oct 19 2026 - 10:48:49 EST
From: "Ewan D. Milne" <emilne@xxxxxxxxxx>
[ Upstream commit f06a44e235ef188689ba23ffc72e9e89b10951a9 ]
EMC Symmetrix returns an error on MODE SENSE for page 0Ah subpage 05h
because it does not implement the SBC-5 I/O hints. These commands began to
be sent as a result of commit 4f53138fffc2 ("scsi: sd: Translate data
lifetime information"). Add BLIST_SKIP_IO_HINTS to avoid sending these
commands because in large configurations the failed commands are displacing
other useful information in internal error logs.
Signed-off-by: Ewan D. Milne <emilne@xxxxxxxxxx>
Link: https://patch.msgid.link/20260915173800.39117-1-emilne@xxxxxxxxxx
Signed-off-by: Martin K. Petersen (Oracle) <mkp@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
LLM Generated explanations, may be completely bogus:
## Local tree
This checkout is **6.18.y** (`v6.18.57-155-gcdf239ca885b2`, `VERSION=6`
/ `PATCHLEVEL=18` / `SUBLEVEL=57`). The verdict is only for this tree.
The I/O-hints path and `BLIST_SKIP_IO_HINTS` are already here. At
`v6.18`, the EMC `SYMMETRIX` blacklist entry does **not** skip those
queries, so the bug exists.
---
## PHASE 1: COMMIT MESSAGE FORENSICS
**Step 1.1: Subject**
- Record: **[scsi/devinfo] [Add] hardware blacklist flag
`BLIST_SKIP_IO_HINTS` for EMC Symmetrix**
**Step 1.2: Tags**
- Record:
- `Signed-off-by: Ewan D. Milne <emilne@xxxxxxxxxx>` (author, Red Hat
SCSI)
- `Link:
https://patch.msgid.link/20260915173800.39117-1-emilne@xxxxxxxxxx`
- `Signed-off-by: Martin K. Petersen (Oracle) <mkp@xxxxxxxxxx>` (SCSI
maintainer)
- No `Fixes:`, `Reported-by:`, `Tested-by:`, `Cc: stable` (absence is
expected)
- Pipeline `Signed-off-by: Sasha Levin` and `[Upstream commit …]`
ignored
**Step 1.3: Body**
- Record: **Bug:** EMC Symmetrix does not implement SBC-5 I/O hints, so
`MODE SENSE` page `0Ah` subpage `05h` fails. Those commands started
after `4f53138fffc2` ("scsi: sd: Translate data lifetime
information").
- **Symptom:** In large configs, failed commands fill the array’s
internal error logs and displace useful entries.
- **Root cause:** Kernel probes a mode page the device does not
implement.
- **Version info:** The probing started with `4f53138fffc2`
(`v6.9-rc1`); that commit is an ancestor of this tree.
**Step 1.4: Hidden bug fix?**
- Record: **No disguise.** This is an explicit hardware quirk. It is not
cleanup/refactor.
---
## PHASE 2: DIFF ANALYSIS
**Step 2.1: Inventory**
- Record: **1 file**, `drivers/scsi/scsi_devinfo.c`, **+1 / -1**, one
table entry.
- Function: static `scsi_dev_info_list` initializer (EMC `SYMMETRIX`
row).
- Scope: **single-file surgical quirk**.
**Step 2.2: Code flow**
- Record: **Before:** flags `BLIST_SPARSELUN | BLIST_LARGELUN |
BLIST_REPORTLUN2 | BLIST_RETRY_ITF`.
- **After:** same plus `BLIST_SKIP_IO_HINTS`.
- Affected path: `sd_read_io_hints()` during `sd_revalidate_disk()`
(probe, open/revalidate, rescan). With the flag set it returns
immediately and does not send `MODE SENSE 0x0A/0x05`.
**Step 2.3: Bug mechanism**
- Record: **[Hardware workaround]** Device-specific skip of an
unsupported SCSI mode page. Same pattern as USB storage and the Iomega
ZIP `BLIST_SKIP_IO_HINTS` entries already in this tree.
**Step 2.4: Fix quality**
- Record: **Obviously correct.** One flag bit on an existing
vendor/product match. Regression risk is **very low**: only EMC
`SYMMETRIX` skips a feature it does not implement. No API, locking, or
allocation changes.
---
## PHASE 3: GIT HISTORY
**Step 3.1: Blame**
- Record: EMC `SYMMETRIX` row is old (`3441afc672bc` / `29cfc2ab71d96`
for `BLIST_RETRY_ITF`, 2018). The **new** failure is not that row; it
is `sd_read_io_hints()` from `4f53138fffc2` (**v6.9-rc1**,
2024-02-26).
**Step 3.2: Fixes: tag**
- Record: **None.** The message names `4f53138fffc2`. `git merge-base
--is-ancestor 4f53138fffc2 HEAD` → **yes**. `git describe --contains
4f53138fffc2` → `v6.9-rc1~12^2~8`.
**Step 3.3: File history**
- Record: Related: `74b25178943fe` ("scsi: devinfo: Add
BLIST_SKIP_IO_HINTS for Iomega ZIP") — same quirk class, already in
this 6.18 tree. `633aeefafc9c2` introduced the flag (**v6.10-rc5**),
also an ancestor. **Standalone**, not patch X/Y.
**Step 3.4: Author**
- Record: Ewan D. Milne is a long-time SCSI contributor (Red Hat).
Applied by SCSI maintainer Martin K. Petersen. Related flag work by
Bart Van Assche (`BLIST_SKIP_IO_HINTS` intro, `Cc: stable` there).
**Step 3.5: Prerequisites**
- Record: Needs `BLIST_SKIP_IO_HINTS` and `sd_read_io_hints()` skip
check. Both exist in `v6.18` (`include/scsi/scsi_devinfo.h:73`,
`drivers/scsi/sd.c:3235`). **Applies standalone.**
---
## PHASE 4: MAILING LIST / EXTERNAL
**Step 4.1: Original discussion**
- Record: `b4 dig -c f06a44e235ef` →
https://patch.msgid.link/20260915173800.39117-1-emilne@xxxxxxxxxx
- **v1 only** (`b4 dig -a`). No NAKs. Laurence Oberman: “Looks good” +
`Reviewed-by`. Martin Petersen: applied to **7.3/scsi-fixes**
(`https://git.kernel.org/mkp/scsi/c/f06a44e235ef`). No `Cc: stable` in
review.
**Step 4.2: Recipients (`b4 dig -w`)**
- Record: Author + `linux-scsi@xxxxxxxxxxxxxxx`. SCSI list was CCed;
maintainer applied it.
**Step 4.3: Bug report**
- Record: No syzbot/bugzilla. Description is operational: array error-
log overflow in large configs. That is a real enterprise SAN issue,
not a theoretical one.
**Step 4.4: Series**
- Record: **Standalone 1/1.** ZIP quirk is a sibling pattern, not a
dependency.
**Step 4.5: Stable list**
- Record: No lore.kernel.org/stable hit for this subject. WebFetch to
lore returned 403; stable search via WebSearch found nothing relevant.
---
## PHASE 5: CODE SEMANTIC ANALYSIS
**Step 5.1: Functions**
- Record: No function body change. Table consumed via
`sdev->sdev_bflags`. Consumer: `sd_read_io_hints()`.
**Step 5.2: Callers**
- Record: `sd_read_io_hints()` is called only from
`sd_revalidate_disk()` (`drivers/scsi/sd.c:3773`).
- `sd_revalidate_disk()` is called from:
- `sd_probe()` (disk attach)
- `sd_open()` if `sd_need_revalidate()`
- `sd_rescan()`
- sysfs cache-type store path
- **Process context**, SCSI disk attach/revalidate. In a large Symmetrix
config this runs once per LUN (often thousands).
**Step 5.3: Callees**
- Record: Without the flag, `scsi_mode_sense(..., modepage=0x0a,
subpage=0x05, ...)`. On failure (`res < 0`) it already returns; the
kernel does not oops. Harm is the failed command on the array.
**Step 5.4: Reachability**
- Record: **Yes.** Any EMC Symmetrix LUN probed as `sd` hits this. Not
an obscure config path.
**Step 5.5: Similar patterns**
- Record: USB storage/`uas` set `BLIST_SKIP_IO_HINTS` because some
devices **reset** on that page. Iomega ZIP uses it because the query
makes the drive unusable. Same skip, milder Symmetrix symptom (error-
log flood).
---
## PHASE 6: LOCAL TREE CROSS-REFERENCE
**Step 6.1: Buggy code in this tree?**
- Record: **Yes.** `v6.18` has `sd_read_io_hints()` and the flag check,
and the EMC row **without** `BLIST_SKIP_IO_HINTS`. Bug since
`4f53138fffc2` (v6.9), so it is in 6.18.
**Step 6.2: Backport difficulty**
- Record: **Clean apply.** Parent of the candidate still has the same
two-line EMC entry as `v6.18`. No refactor of that table.
**Step 6.3: Related fixes already here?**
- Record: Flag infrastructure and ZIP/USB skips are present. **No**
existing skip for EMC Symmetrix at `v6.18`.
---
## PHASE 7: SUBSYSTEM CONTEXT
**Step 7.1**
- Record: **[SCSI disk / scsi_devinfo] [IMPORTANT]** — not core mm/VFS,
but enterprise block storage. EMC/Dell Symmetrix (VMAX/PowerMax
lineage) is still used on LTS kernels.
**Step 7.2**
- Record: SCSI is actively maintained; this file is a mature quirk
table, not a new subsystem.
---
## PHASE 8: IMPACT AND RISK
**Step 8.1: Who is affected**
- Record: **Driver/hardware-specific:** hosts with `INQUIRY` vendor
`EMC` / product `SYMMETRIX`. Typical: datacenter SAN on 6.18 LTS.
**Step 8.2: Trigger**
- Record: **Every disk revalidate** (probe, rescan, some opens). Common
on boot and device discovery. Unprivileged users do not trigger it
directly; udev/scan does. Not a race.
**Step 8.3: Failure mode**
- Record: **Not a kernel oops.** Failed `MODE SENSE` is ignored in
`sd_read_io_hints()`. User-visible issue is **array error-log
pollution** in large LUN counts, hiding real faults. Severity
**MEDIUM** for the kernel, **HIGH** operationally on big arrays.
USB/ZIP cases of the same flag were crash/unusable-device; this is the
same class of quirk.
**Step 8.4: Risk/benefit**
- Record: **Benefit: high for Symmetrix users, zero for others. Risk:
very low (1 flag bit, existing match).** Ratio favors backport.
---
## PHASE 9: SYNTHESIS
**Step 9.1: Evidence**
For:
- Real hardware incompatibility with a command 6.18 already sends
- Enterprise arrays, large LUN counts, error-log displacement
- 1-line quirk; `BLIST_SKIP_IO_HINTS` already in this tree
- Same class as USB/ZIP skips; ZIP already on 6.18
- Reviewed and applied to scsi-fixes by the SCSI maintainer
- Applies cleanly to `v6.18`
Against:
- Not a kernel crash, UAF, deadlock, or data corruption
- No `Cc: stable` / `Fixes:`
- Affects only one vendor/product
Unresolved:
- Lore HTTP 403; thread recovered via `b4 dig -m`. No public
syzbot/bugzilla count of affected arrays.
**Step 9.2: Stable rules**
1. Obviously correct and tested? **PASS** — 1-bit flag; maintainer
applied; `Reviewed-by: Laurence Oberman`
2. Real bug affecting users? **PASS** — unsupported `MODE SENSE` on
production arrays
3. Important issue? **PASS** as a hardware quirk (array log overflow in
large configs). Not a kernel panic.
4. Small and contained? **PASS** — +1/-1, one table row
5. No new features/APIs? **PASS** — uses existing flag
6. Can apply to this tree? **PASS** — flag, consumer, and EMC row all
present at `v6.18`
**Step 9.3: Exception**
- Record: **Hardware quirk/workaround** (scsi_devinfo blacklist),
analogous to USB/PCI quirks. That class is accepted for stable.
**Step 9.4: Decision**
This is a one-line device quirk for hardware this 6.18 tree already
probes with I/O-hints `MODE SENSE`. The skip flag and call site exist;
the EMC row does not skip yet. Risk is negligible; benefit is real for
Symmetrix/VMAX deployments. **YES for this tree.**
---
## What this solves for 6.18 users
Since v6.9, `sd_revalidate_disk()` calls `sd_read_io_hints()`, which
issues `MODE SENSE` page 0x0A subpage 0x05. EMC Symmetrix does not
implement that SBC-5 page and returns an error. The kernel already
swallows the error; on arrays with many LUNs those failures fill the
controller’s error logs. Adding `BLIST_SKIP_IO_HINTS` stops the query
for that INQUIRY match only.
It meets stable rules: small, obviously correct, no new API, applies
cleanly, and is a standard scsi_devinfo hardware quirk.
---
## Verification
- **[Phase 1]** Parsed tags: author SOB Ewan Milne, Link to msgid,
maintainer SOB Martin Petersen; no Fixes/Reported-by/Cc:stable
- **[Phase 2]** Diff: 1 line in `scsi_devinfo.c` EMC SYMMETRIX flags;
adds `BLIST_SKIP_IO_HINTS`
- **[Phase 3]** `git describe HEAD` / `make kernelversion`: **6.18.57**
- **[Phase 3]** `git merge-base --is-ancestor 4f53138fffc2 HEAD`: yes;
`git describe --contains`: v6.9-rc1
- **[Phase 3]** `git merge-base --is-ancestor 633aeefafc9c2 HEAD`: yes
(flag intro, v6.10-rc5)
- **[Phase 3]** `git blame` EMC row: `29cfc2ab71d96` added
`BLIST_RETRY_ITF` (2018); skip flag is new
- **[Phase 3]** `git show v6.18:drivers/scsi/scsi_devinfo.c`: SYMMETRIX
**without** `BLIST_SKIP_IO_HINTS`
- **[Phase 3]** `git grep BLIST_SKIP_IO_HINTS v6.18`: flag and `sd.c`
check present
- **[Phase 4]** `b4 dig -c f06a44e235ef`: lore URL; v1 only; Reviewed-by
Laurence Oberman; applied to 7.3/scsi-fixes
- **[Phase 4]** `b4 dig -m`: full thread, no NAK, no stable nomination
- **[Phase 4]** WebFetch lore/msgid: **403**; used b4 mbox instead
- **[Phase 5]** Callers: `sd_read_io_hints` ← `sd_revalidate_disk` ←
`sd_probe` / `sd_open` / `sd_rescan`
- **[Phase 6]** Parent of candidate matches `v6.18` EMC lines → clean
apply
- **[Phase 8]** Failure: array error-log flood, not kernel oops;
severity MEDIUM kernel / HIGH operational
- **UNVERIFIED:** Exact customer ticket / number of arrays (not in the
thread)
**YES**
drivers/scsi/scsi_devinfo.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
index c51146882a1fa..a438e510f2cae 100644
--- a/drivers/scsi/scsi_devinfo.c
+++ b/drivers/scsi/scsi_devinfo.c
@@ -161,7 +161,7 @@ static struct {
{"DGC", "DISK", NULL, BLIST_SPARSELUN}, /* EMC CLARiiON, no storage on LUN 0 */
{"EMC", "Invista", "*", BLIST_SPARSELUN | BLIST_LARGELUN},
{"EMC", "SYMMETRIX", NULL, BLIST_SPARSELUN | BLIST_LARGELUN |
- BLIST_REPORTLUN2 | BLIST_RETRY_ITF},
+ BLIST_REPORTLUN2 | BLIST_RETRY_ITF | BLIST_SKIP_IO_HINTS},
{"EMULEX", "MD21/S2 ESDI", NULL, BLIST_SINGLELUN},
{"easyRAID", "16P", NULL, BLIST_NOREPORTLUN},
{"easyRAID", "X6P", NULL, BLIST_NOREPORTLUN},
--
2.53.0