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Description: zfcp: Fix panic on ERP timeout for previously dismissed ERP
Symptom: Linux kernel panic due to kernel page fault in IRQ context
when running zfcp_erp_timeout_handler() calling
zfcp_erp_notify().
Problem: Suppose that, for unrelated reasons, FSF requests on behalf
of recovery are very slow and can run into the ERP timeout.
In the case at hand, we did adapter recovery to a large
degree. However due to the slowness a LUN open is pending so
the corresponding fc_rport remains blocked. After
fast_io_fail_tmo we trigger close physical port recovery for
the port under which the LUN should have been opened. The
new higher order port recovery dismisses the pending LUN
open ERP action and dismisses the pending LUN open FSF
request. Such dismissal decouples the ERP action from the
pending corresponding FSF request by setting
zfcp_fsf_req->erp_action to NULL (among other things)
[zfcp_erp_strategy_check_fsfreq()].
If now the ERP timeout for the pending open LUN request runs
out, we must not use zfcp_fsf_req->erp_action in the ERP
timeout handler. This is a problem since v4.15 commit
75492a51568b ("s390/scsi: Convert timers to use
timer_setup()"). Before that we intentionally only passed
zfcp_erp_action as context argument to
zfcp_erp_timeout_handler().
Note: The lifetime of the corresponding zfcp_fsf_req object
continues until a (late) response or an (unrelated) adapter
recovery.
Solution: Just like the regular response path ignores dismissed
requests [zfcp_fsf_req_complete() =>
zfcp_fsf_protstatus_eval() => return early] the ERP timeout
handler now needs to ignore dismissed requests. So simply
return early in the ERP timeout handler if the FSF request
is marked as dismissed in its status flags. To protect
against the race where zfcp_erp_strategy_check_fsfreq()
dismisses and sets zfcp_fsf_req->erp_action to NULL after
our previous status flag check, return early if
zfcp_fsf_req->erp_action is NULL. After all, the former ERP
action does not need to be woken up as that was already done
as part of the dismissal above [zfcp_erp_action_dismiss()].
Upstream-ID: 936e6b85da0476dd2edac7c51c68072da9fb4ba2 -> kernel 5.8
Will be integrated by kernel 5.8 by groovy.
Please check that this also be integrated into 20.04
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Tags: architecture-s39064 bugnameltc-186883 severity-high
targetmilestone-inin20041
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[UBUNTU 20.04] zfcp: Fix panic on ERP timeout for previously dismissed ERP
https://bugs.launchpad.net/bugs/1887774
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