[PATCH v8 0/2] libsas: rediscover improvements for linkrate/sas_addr changes

[Xingui Yang <yangxingui@huawei.com>]

When a device attached to an expander phy experiences a linkrate change
(e.g., due to cable reconnection or negotiation), the current code in
sas_rediscover_dev() treats it as "broadcast flutter" and takes no action
if the SAS address and device type remain unchanged.

This series is based on John Garry's suggestion [1] to check the linkrate
and mark the device as gone and rediscover when flutter occurs, replacing
the previous v2 patch series that used lldd callbacks.

The previous v2 approach added lldd_dev_info_update callback which John
commented as "seem fragile and too specialized" [2]. This series adopts
a simpler approach that directly checks linkrate/sas_addr changes in
sas_rediscover_dev() and triggers rediscovery using libsas's standard
async discovery pattern.

This aligns with Jason Yan's earlier work [3] which was verified to
solve the linkrate change issue.

Additionally, per the discussion in v3 [4], the existing replace code
path also suffers from the same sysfs duplication issue:
sas_unregister_devs_sas_addr() only marks the device as gone, but the
actual sysfs cleanup happens later in sas_destruct_devices(). Calling
sas_discover_new() immediately after unregister causes sysfs_warn_dup()
errors. This series also optimizes the replace path to use the async
pattern, ensuring proper ordering for both flutter and replace cases.

Changes from v7:
Addressed issues identified by Sashiko AI review [5][6]:
- In sas_dev_is_flutter(), reorder sas_addr check before linkrate check
  to ensure address restoration is not skipped when both change
  simultaneously, preventing device leak
- In sas_dev_is_flutter(), hold a kref on child_dev across the
  sas_ex_phy_discover() call to prevent use-after-free
- In sas_ex_to_dev(), add defensive NULL check for ex_dev to guard
  against callers passing a NULL device

Not addressed (pre-existing subsystem design):
- sas_find_dev_by_rphy() returns unreferenced pointer: subsystem-wide
  pattern used by 10+ call sites, should be a separate patch
- ex_phy->port TOCTOU: discovery path is serialized by disco_mutex,
  no race occurs in practice

Changes from v6:
- Add comment for restoring phy->attached_sas_addr to child_dev->sas_addr
- Optimize the conditional structure in sas_dev_is_flutter()

Changes from v5:
- In sas_addr change handling, restore phy->attached_sas_addr to
  child_dev->sas_addr before returning false, ensuring
  sas_unregister_devs_sas_addr() can properly match the device via
  sas_phy_match_dev_addr() for correct device unregistration

Changes from v4:
- Rename sas_rediscover_phy to sas_rediscover_ex_phy for consistency
  with expander phy symbol naming convention
- Rename sas_is_flutter to sas_dev_is_flutter per John's suggestion
- Check return value of sas_ex_phy_discover() for errors
- Factor out child_dev checks to improve code clarity

Changes from v3:
- Also optimize the replace code path to use async discovery pattern
- Introduce sas_is_flutter() and sas_rediscover_phy() helpers
  to encapsulate the flutter handling logic and avoid function bloat
- Fix replace code path sysfs duplication issue

Changes from v2:
- Drop lldd_dev_info_update callback approach per John Garry's suggestion
- Drop hisi_sas specific changes (no longer needed without callback)
- Use libsas's async discovery pattern for rediscovery
- Add sas_addr change detection alongside linkrate change

Changes from v1:
- Split into three patches

[1] https://lore.kernel.org/linux-scsi/c4e4c99f-a13c-4e28-8650-48be1f96d7cf@oracle.com/
[2] https://lore.kernel.org/linux-scsi/28bd9d5b-f597-0aae-5340-bd951b2083aa@huawei.com/
[3] https://lore.kernel.org/linux-scsi/20190130082412.9357-6-yanaijie@huawei.com/
[4] https://lore.kernel.org/linux-scsi/b99cd59f-b986-432e-aaf1-3b757e1c4c34@oracle.com/
[5] https://lore.kernel.org/linux-scsi/20260611062530.3B6651F00898@smtp.kernel.org/
[6] https://lore.kernel.org/linux-scsi/20260611062833.357031F00893@smtp.kernel.org/

Xingui Yang (2):
  scsi: libsas: refactor sas_ex_to_ata() using new helper
    sas_ex_to_dev()
  scsi: libsas: Add linkrate and sas_addr change detection in rediscover

 drivers/scsi/libsas/sas_expander.c | 107 ++++++++++++++++++++++++-----
 drivers/scsi/libsas/sas_internal.h |   1 +
 2 files changed, 89 insertions(+), 19 deletions(-)

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2.43.0