ba81043753
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 0e9d4ca43ba8 ("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
87bd05016a64 ("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: 0e9d4ca43ba8 ("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>
Linux kernel
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