[PATCH v4 0/2] scsi: ufs: core: Avoid redundant link recovery from the error handler during PM

[HOYOUNG SEO <hy50.seo@samsung.com>]

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 restricts the early link recovery in ufshcd_err_handler(), which
does not hold host_sem, to runtime PM. For system PM the error handler
now waits for host_sem, and for shutdown it stops.

The early link recovery is kept for runtime suspend and runtime resume.
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 v4 (as suggested by Bart Van Assche):
- Replace the is_sys_suspended check of v3 patch 2 with a check for
  runtime PM, which also covers system suspend failure and shutdown.
- 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.

v3: https://lore.kernel.org/linux-scsi/cover.1792989286.git.hy50.seo@samsung.com/
v2: https://lore.kernel.org/linux-scsi/cover.1792755091.git.hy50.seo@samsung.com/

HOYOUNG SEO (2):
  scsi: ufs: core: Clear saved errors in ufshcd_link_recovery
  scsi: ufs: core: Limit early link recovery in the error handler to
    runtime PM

 drivers/ufs/core/ufshcd.c | 29 +++++++++++++++++++++++++----
 include/ufs/ufshcd.h      |  2 ++
 2 files changed, 27 insertions(+), 4 deletions(-)

-- 
2.34.1