[PATCH v5 0/2] scsi: ufs: core: Avoid redundant link recovery from the error handler during system PM

[HOYOUNG SEO]

If a LINERESET is reported and the hibern8 exit fails during system
resume, both ufshcd_err_handler() and __ufshcd_wl_resume() call
ufshcd_link_recovery(), and the two recoveries are not serialized.

Patch 1 makes ufshcd_link_recovery() clear the saved errors like
ufshcd_reset_and_restore() does, so the error handler does not act on
errors that have already been recovered.

Patch 2 skips the early link recovery in ufshcd_err_handler(), which
does not hold host_sem, while a system PM operation is in progress. The
system PM callbacks hold host_sem, so the error handler now waits for
them.

The early link recovery is kept for runtime PM, shutdown and poweroff,
which do not hold host_sem. During runtime resume it can still run
concurrently with __ufshcd_wl_resume(). Removing it there needs a closer
look at the deadlock that it avoids.

Changes in v5:
- Patch 2: track system PM (hba->system_pm_in_progress) instead of
  runtime PM, so that the early link recovery is only skipped where
  host_sem is held. ufshcd_wl_poweroff() holds neither host_sem nor sets
  hba->shutting_down, so poweroff keeps the early link recovery as
  before (Sashiko review).

Changes in v4 (as suggested by Bart Van Assche):
- Replace the is_sys_suspended check of v3 patch 2 with a flag set in
  __ufshcd_wl_suspend() and __ufshcd_wl_resume(), which also covers a
  system suspend failure.
- Add Fixes: tags.
- Do not serialize ufshcd_link_recovery() with a mutex: it calls
  ufshcd_probe_hba(), and a device command timing out inside it ends up
  in ufshcd_eh_timed_out(), which calls ufshcd_link_recovery() again.

Changes in v3:
- Patch 2: reword the commit message only, no code change. The error
  handler does not always run a full recovery after a failed system
  resume; it stops according to ufshcd_err_handling_should_stop() (e.g.
  in UFSHCD_STATE_ERROR). Describe this behavior and refer to the commit
  that added the early link recovery (Sashiko review).
- Patch 1: no change.

Changes in v2:
- Add patch 1. As pointed out by the Sashiko review, saved_err and
  saved_uic_err are still set after the resume path recovered the link,
  so with v1 alone ufshcd_err_handler() would run a redundant recovery
  once host_sem is released.
- Patch 2: describe the race and the system/runtime PM difference in
  the commit message, and add a comment.

v4: https://lore.kernel.org/linux-scsi/cover.1793851432.git.hy50.seo@xxxxxxxxxxx/
v3: https://lore.kernel.org/linux-scsi/cover.1792989286.git.hy50.seo@xxxxxxxxxxx/
v2: https://lore.kernel.org/linux-scsi/cover.1792755091.git.hy50.seo@xxxxxxxxxxx/

HOYOUNG SEO (2):
  scsi: ufs: core: Clear saved errors in ufshcd_link_recovery
  scsi: ufs: core: Do not recover the link early in the error handler
    during system PM

 drivers/ufs/core/ufshcd.c | 25 +++++++++++++++++++++++--
 include/ufs/ufshcd.h      |  2 ++
 2 files changed, 25 insertions(+), 2 deletions(-)

-- 
2.34.1