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scsi: ufs: core: Fix devfreq deadlocks
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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 0e9d4ca ("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
87bd050 ("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 Rust-for-Linux#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: 0e9d4ca ("scsi: ufs: Protect some contexts from unexpected clock scaling")
Cc: [email protected]      # 5.12
Cc: Can Guo <[email protected]>
Tested-by: Andrew Halaney <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>
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@jhovold @martinkpetersen
jhovold authored and martinkpetersen committed Jan 19, 2023
1 parent bbbd254 commit ba81043
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Showing 2 changed files with 17 additions and 14 deletions.
29 changes: 15 additions & 14 deletions drivers/ufs/core/ufshcd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1234,12 +1234,14 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
* clock scaling is in progress
*/
ufshcd_scsi_block_requests(hba);
mutex_lock(&hba->wb_mutex);
down_write(&hba->clk_scaling_lock);

if (!hba->clk_scaling.is_allowed ||
ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
ret = -EBUSY;
up_write(&hba->clk_scaling_lock);
mutex_unlock(&hba->wb_mutex);
ufshcd_scsi_unblock_requests(hba);
goto out;
}
Expand All @@ -1251,12 +1253,16 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
return ret;
}

static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, int err, bool scale_up)
{
if (writelock)
up_write(&hba->clk_scaling_lock);
else
up_read(&hba->clk_scaling_lock);
up_write(&hba->clk_scaling_lock);

/* Enable Write Booster if we have scaled up else disable it */
if (ufshcd_enable_wb_if_scaling_up(hba) && !err)
ufshcd_wb_toggle(hba, scale_up);

mutex_unlock(&hba->wb_mutex);

ufshcd_scsi_unblock_requests(hba);
ufshcd_release(hba);
}
Expand All @@ -1273,7 +1279,6 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
{
int ret = 0;
bool is_writelock = true;

ret = ufshcd_clock_scaling_prepare(hba);
if (ret)
Expand Down Expand Up @@ -1302,15 +1307,8 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
}
}

/* Enable Write Booster if we have scaled up else disable it */
if (ufshcd_enable_wb_if_scaling_up(hba)) {
downgrade_write(&hba->clk_scaling_lock);
is_writelock = false;
ufshcd_wb_toggle(hba, scale_up);
}

out_unprepare:
ufshcd_clock_scaling_unprepare(hba, is_writelock);
ufshcd_clock_scaling_unprepare(hba, ret, scale_up);
return ret;
}

Expand Down Expand Up @@ -6066,9 +6064,11 @@ static void ufshcd_force_error_recovery(struct ufs_hba *hba)

static void ufshcd_clk_scaling_allow(struct ufs_hba *hba, bool allow)
{
mutex_lock(&hba->wb_mutex);
down_write(&hba->clk_scaling_lock);
hba->clk_scaling.is_allowed = allow;
up_write(&hba->clk_scaling_lock);
mutex_unlock(&hba->wb_mutex);
}

static void ufshcd_clk_scaling_suspend(struct ufs_hba *hba, bool suspend)
Expand Down Expand Up @@ -9793,6 +9793,7 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
/* Initialize mutex for exception event control */
mutex_init(&hba->ee_ctrl_mutex);

mutex_init(&hba->wb_mutex);
init_rwsem(&hba->clk_scaling_lock);

ufshcd_init_clk_gating(hba);
Expand Down
2 changes: 2 additions & 0 deletions include/ufs/ufshcd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -808,6 +808,7 @@ struct ufs_hba_monitor {
* @urgent_bkops_lvl: keeps track of urgent bkops level for device
* @is_urgent_bkops_lvl_checked: keeps track if the urgent bkops level for
* device is known or not.
* @wb_mutex: used to serialize devfreq and sysfs write booster toggling
* @clk_scaling_lock: used to serialize device commands and clock scaling
* @desc_size: descriptor sizes reported by device
* @scsi_block_reqs_cnt: reference counting for scsi block requests
Expand Down Expand Up @@ -951,6 +952,7 @@ struct ufs_hba {
enum bkops_status urgent_bkops_lvl;
bool is_urgent_bkops_lvl_checked;

struct mutex wb_mutex;
struct rw_semaphore clk_scaling_lock;
unsigned char desc_size[QUERY_DESC_IDN_MAX];
atomic_t scsi_block_reqs_cnt;
Expand Down

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