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Adrian Hunter 88b099006d scsi: ufs: core: Revert "scsi: ufs: Synchronize SCSI and UFS error handling" 
This reverts commit a113eaaf86.

There are a couple of issues with the commit:

 1. It causes deadlocks.

 2. It causes the shost->eh_cmd_q list of failed requests not to be
    processed, ever.

So revert it.

1. Deadlocks

The SCSI error handler runs with requests blocked beginning when
scsi_schedule_eh() sets SHOST_RECOVERY state, continuing through
scsi_error_handler() callback ->eh_strategy_handler() until
scsi_restart_operations() is called.  By setting eh_strategy_handler to
ufshcd_err_handler, the patch changed the UFS error handler to run with
requests blocked, including PM requests, for the entire run of the error
handler.

That conflicts with UFS error handler existing synchronization with UFS
device PM operations.  The UFS error handler synchronizes with runtime PM
by doing pm_runtime_get_sync() prior to blocking requests itself.  It
synchronizes with system PM by use of hba->host_sem, again before blocking
requests itself.  However, if requests are already blocked, then PM
operations will block.  So:

   the UFS error handler blocks waiting on PM
 + PM blocks waiting on SCSI PM requests to process or fail
 + PM requests are blocked waiting on error handling to finish
 =  deadlock

This happens both for runtime PM and system PM.

Prior to the patch, these deadlocks could not happen even if SCSI error
handling was running, because the presence of requests in shost->eh_cmd_q
would mean the queues could not be suspended, which would mean that, should
the UFS error handler run at the same time, it would not need to wait for
PM or vice versa.

Please note these scenarios are not just theoretical, they were found
during testing on a Samsung Galaxy Book S.

2. ->eh_strategy_handler() must process shost->eh_cmd_q list of failed
requests, as all other eh_strategy_handler's do except UFS error handler.
Refer for example: scsi_unjam_host(), ata_scsi_error() and
sas_scsi_recover_host().

Link: https://lore.kernel.org/r/20210917144349.14058-1-adrian.hunter@intel.com
Fixes: a113eaaf86 ("scsi: ufs: Synchronize SCSI and UFS error handling")
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
History 2021-09-21 23:48:14 -04:00
arch Updates for the SMP and CPU hotplug: 2021-09-12 12:42:51 -07:00
block scsi: bsg: Fix device unregistration 2021-09-14 00:22:15 -04:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-08-30 12:57:10 -07:00
Documentation An assortment of improvements for auxdisplay: 2021-09-12 16:00:49 -07:00
drivers scsi: ufs: core: Revert "scsi: ufs: Synchronize SCSI and UFS error handling" 2021-09-21 23:48:14 -04:00
fs Merge branch 'misc.namei' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2021-09-12 10:43:51 -07:00
include Compiler Attributes improvements: 2021-09-12 16:09:26 -07:00
init More tracing updates for 5.15: 2021-09-09 13:11:15 -07:00
ipc ARM development updates for 5.15: 2021-09-09 13:25:49 -07:00
kernel - Make sure the idle timer expires in hardirq context, on PREEMPT_RT 2021-09-12 11:37:41 -07:00
lib Minor fixes to the processing of the bootconfig tree. 2021-09-11 10:16:30 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm ARM development updates for 5.15: 2021-09-09 13:25:49 -07:00
net virtio,vdpa,vhost: features, fixes 2021-09-11 14:48:42 -07:00
samples kgdb patches for 5.15 2021-09-07 12:08:04 -07:00
scripts RISC-V Patches for the 5.15 Merge Window, Part 2 2021-09-11 14:29:42 -07:00
security Kbuild updates for v5.15 2021-09-03 15:33:47 -07:00
sound sound fixes for 5.15-rc1 2021-09-09 16:05:10 -07:00
tools perf tools changes for v5.15: 2nd batch 2021-09-12 16:18:15 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Drop unused kvm_dirty_gfn_invalid() 2021-09-06 08:23:46 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update email address of Matthias Fuchs and Thomas Körper 2021-08-19 09:39:44 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS scsi: Remove SCSI CDROM MAINTAINERS entry 2021-09-13 22:15:48 -04:00
Makefile Linux 5.15-rc1 2021-09-12 16:28:37 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.