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Johan Hovold ba81043753 scsi: ufs: core: Fix devfreq deadlocks 
There is a lock inversion and rwsem read-lock recursion in the devfreq
target callback which can lead to deadlocks.

Specifically, ufshcd_devfreq_scale() already holds a clk_scaling_lock
read lock when toggling the write booster, which involves taking the
dev_cmd mutex before taking another clk_scaling_lock read lock.

This can lead to a deadlock if another thread:

  1) tries to acquire the dev_cmd and clk_scaling locks in the correct
     order, or

  2) takes a clk_scaling write lock before the attempt to take the
     clk_scaling read lock a second time.

Fix this by dropping the clk_scaling_lock before toggling the write booster
as was done before commit 0e9d4ca43b ("scsi: ufs: Protect some contexts
from unexpected clock scaling").

While the devfreq callbacks are already serialised, add a second
serialising mutex to handle the unlikely case where a callback triggered
through the devfreq sysfs interface is racing with a request to disable
clock scaling through the UFS controller 'clkscale_enable' sysfs
attribute. This could otherwise lead to the write booster being left
disabled after having disabled clock scaling.

Also take the new mutex in ufshcd_clk_scaling_allow() to make sure that any
pending write booster update has completed on return.

Note that this currently only affects Qualcomm platforms since commit
87bd05016a ("scsi: ufs: core: Allow host driver to disable wb toggling
during clock scaling").

The lock inversion (i.e. 1 above) was reported by lockdep as:

 ======================================================
 WARNING: possible circular locking dependency detected
 6.1.0-next-20221216 #211 Not tainted
 ------------------------------------------------------
 kworker/u16:2/71 is trying to acquire lock:
 ffff076280ba98a0 (&hba->dev_cmd.lock){+.+.}-{3:3}, at: ufshcd_query_flag+0x50/0x1c0

 but task is already holding lock:
 ffff076280ba9cf0 (&hba->clk_scaling_lock){++++}-{3:3}, at: ufshcd_devfreq_scale+0x2b8/0x380

 which lock already depends on the new lock.
[  +0.011606]
 the existing dependency chain (in reverse order) is:

 -> #1 (&hba->clk_scaling_lock){++++}-{3:3}:
        lock_acquire+0x68/0x90
        down_read+0x58/0x80
        ufshcd_exec_dev_cmd+0x70/0x2c0
        ufshcd_verify_dev_init+0x68/0x170
        ufshcd_probe_hba+0x398/0x1180
        ufshcd_async_scan+0x30/0x320
        async_run_entry_fn+0x34/0x150
        process_one_work+0x288/0x6c0
        worker_thread+0x74/0x450
        kthread+0x118/0x120
        ret_from_fork+0x10/0x20

 -> #0 (&hba->dev_cmd.lock){+.+.}-{3:3}:
        __lock_acquire+0x12a0/0x2240
        lock_acquire.part.0+0xcc/0x220
        lock_acquire+0x68/0x90
        __mutex_lock+0x98/0x430
        mutex_lock_nested+0x2c/0x40
        ufshcd_query_flag+0x50/0x1c0
        ufshcd_query_flag_retry+0x64/0x100
        ufshcd_wb_toggle+0x5c/0x120
        ufshcd_devfreq_scale+0x2c4/0x380
        ufshcd_devfreq_target+0xf4/0x230
        devfreq_set_target+0x84/0x2f0
        devfreq_update_target+0xc4/0xf0
        devfreq_monitor+0x38/0x1f0
        process_one_work+0x288/0x6c0
        worker_thread+0x74/0x450
        kthread+0x118/0x120
        ret_from_fork+0x10/0x20

 other info that might help us debug this:
  Possible unsafe locking scenario:
        CPU0                    CPU1
        ----                    ----
   lock(&hba->clk_scaling_lock);
                                lock(&hba->dev_cmd.lock);
                                lock(&hba->clk_scaling_lock);
   lock(&hba->dev_cmd.lock);

  *** DEADLOCK ***

Fixes: 0e9d4ca43b ("scsi: ufs: Protect some contexts from unexpected clock scaling")
Cc: stable@vger.kernel.org      # 5.12
Cc: Can Guo <quic_cang@quicinc.com>
Tested-by: Andrew Halaney <ahalaney@redhat.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230116161201.16923-1-johan+linaro@kernel.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
2023-01-18 19:08:37 -05:00
arch treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
block treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto This update includes the following changes: 2022-12-14 12:31:09 -08:00
Documentation kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
drivers scsi: ufs: core: Fix devfreq deadlocks 2023-01-18 19:08:37 -05:00
fs treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
include scsi: ufs: core: Fix devfreq deadlocks 2023-01-18 19:08:37 -05:00
init Kbuild updates for v6.2 2022-12-19 12:33:32 -06:00
io_uring io_uring/net: fix cleanup after recycle 2022-12-19 08:28:28 -07:00
ipc Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
kernel kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
lib test_maple_tree: add test for mas_spanning_rebalance() on insufficient data 2022-12-21 14:31:52 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm hugetlb: really allocate vma lock for all sharable vmas 2022-12-21 14:31:52 -08:00
net treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
rust rust: types: add Opaque type 2022-12-04 01:59:16 +01:00
samples Char/Misc driver changes for 6.2-rc1 2022-12-16 03:49:24 -08:00
scripts modernize use of grep in coccicheck 2022-12-23 13:56:41 -08:00
security kernel hardening fixes for v6.2-rc1 2022-12-23 12:00:24 -08:00
sound treewide: Convert del_timer*() to timer_shutdown*() 2022-12-25 13:38:09 -08:00
tools perf tools fixes and improvements for v6.2: 2nd batch 2022-12-22 11:07:29 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt ARM64: 2022-12-15 11:12:21 -08:00
.clang-format iommufd for 6.2 2022-12-14 09:15:43 -08:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: Cleanup DT Overlay intermediate files as appropriate 2022-11-18 14:45:30 -06:00
.mailmap Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: zram: zsmalloc: Add an additional co-maintainer 2022-12-15 16:37:49 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS io_uring-6.2-2022-12-19 2022-12-21 16:28:25 -08:00
Makefile Linux 6.2-rc1 2022-12-25 13:41:39 -08:00
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.