scsi: ufs: core: Fix a deadlock in the frequency scaling code

Commit 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
accidentally introduced a deadlock in the frequency scaling code.
ufshcd_clock_scaling_unprepare() may submit a device management command
while SCSI command processing is blocked. The deadlock was introduced by
using the SCSI core for submitting device management commands
(scsi_get_internal_cmd() + blk_execute_rq()). Fix this deadlock by calling
blk_mq_unquiesce_tagset() before any device management commands are
submitted by ufshcd_clock_scaling_unprepare().

Fixes: 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
Reported-by: Manivannan Sadhasivam <mani@kernel.org>
Reported-by: Roger Shimizu <rosh@debian.org>
Closes: https://lore.kernel.org/linux-scsi/ehorjaflathzab5oekx2nae2zss5vi2r36yqkqsfjb2fgsifz2@yk3us5g3igow/
Tested-by: Roger Shimizu <rosh@debian.org>
Cc: Nitin Rawat <nitin.rawat@oss.qualcomm.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Peter Wang <peter.wang@mediatek.com>
Reviewed-by: Nitin Rawat <nitin.rawat@oss.qualcomm.com>
Tested-by: Alexey Klimov <alexey.klimov@linaro.org> # RB5 board
Link: https://patch.msgid.link/20251204181548.1006696-1-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 1837ae204d5eb0b42d7358583dc2d4450d261cf7..80c0b49f30b01284d1a392dbea76ed8d4a68ab5b 100644 (file)
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -1455,15 +1455,14 @@ out:
 static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, int err)
 {
        up_write(&hba->clk_scaling_lock);
+       mutex_unlock(&hba->wb_mutex);
+       blk_mq_unquiesce_tagset(&hba->host->tag_set);
+       mutex_unlock(&hba->host->scan_mutex);
 
        /* Enable Write Booster if current gear requires it else disable it */
        if (ufshcd_enable_wb_if_scaling_up(hba) && !err)
                ufshcd_wb_toggle(hba, hba->pwr_info.gear_rx >= hba->clk_scaling.wb_gear);
 
-       mutex_unlock(&hba->wb_mutex);
-
-       blk_mq_unquiesce_tagset(&hba->host->tag_set);
-       mutex_unlock(&hba->host->scan_mutex);
        ufshcd_release(hba);
 }