Re: [PATCH v9 0/2] libsas: rediscover improvements for linkrate/sas_addr changes

Hi, John

Kindly ping for review...

On 2026/6/24 14:32, Xingui Yang wrote:
> 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 v8:
> - In sas_dev_is_flutter(), call sas_ex_phy_discover() before
>    sas_ex_to_dev() to ensure PHY state is always updated and to avoid
>    use-after-free since the child device pointer is obtained after the
>    sleeping SMP request completes, eliminating the need for kref
> - Addressed Sashiko AI review [5][6] feedback on PHY discovery bypass
>    and TOCTOU concerns
> 
> 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_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/[email protected]/
> [2] https://lore.kernel.org/linux-scsi/[email protected]/
> [3] https://lore.kernel.org/linux-scsi/[email protected]/
> [4] https://lore.kernel.org/linux-scsi/[email protected]/
> [5] https://lore.kernel.org/linux-scsi/[email protected]/
> [6] https://lore.kernel.org/linux-scsi/[email protected]/
> 
> 
> 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 | 102 +++++++++++++++++++++++------
>   drivers/scsi/libsas/sas_internal.h |   1 +
>   2 files changed, 84 insertions(+), 19 deletions(-)
>