[PATCH v2] scsi: ufs: core: Avoid possible memory reclaim deadlock in TX EQTR context

[Can Guo]

TX EQTR may run while devfreq gear scaling has quiesced the UFS tagset. In
that context, functions ufshcd_tx_eqtr(), __ufshcd_tx_eqtr() and
ufs_qcom_get_rx_fom() allocate memory with GFP_KERNEL. If direct reclaim
is triggered, reclaim/writeback can depend on I/O to UFS device. Because
the queue is quiesced, this can cause deadlock.

Use memalloc_noio_save/restore() in ufshcd_tx_eqtr() to cover all
allocations in the TX EQTR call tree, including:
- params->eqtr_record in ufshcd_tx_eqtr()
- eqtr_data in __ufshcd_tx_eqtr()
- params in ufs_qcom_get_rx_fom()

This is preferred over tagging individual call sites with GFP_NOIO, as it
automatically covers any future allocations added anywhere in the call
tree without requiring each caller to be aware of this constraint.

Fixes: 03e5d38e2f98 ("scsi: ufs: core: Add support for TX Equalization")
Closes: https://sashiko.dev/#/patchset/20260615132834.2985346-1-can.guo@xxxxxxxxxxxxxxxx?part=2
Signed-off-by: Can Guo <can.guo@xxxxxxxxxxxxxxxx>
---
v1 -> v2:
- Replaced per-allocation GFP_NOIO usage with memalloc_noio_save/restore()
  around ufshcd_tx_eqtr() call tree.

 drivers/ufs/core/ufs-txeq.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/ufs/core/ufs-txeq.c b/drivers/ufs/core/ufs-txeq.c
index 4b264adfdf49..9dca0cd344b8 100644
--- a/drivers/ufs/core/ufs-txeq.c
+++ b/drivers/ufs/core/ufs-txeq.c
@@ -10,6 +10,7 @@
 #include <linux/delay.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
+#include <linux/sched/mm.h>
 #include <ufs/ufshcd.h>
 #include <ufs/unipro.h>
 #include "ufshcd-priv.h"
@@ -1212,14 +1213,25 @@ static int ufshcd_tx_eqtr(struct ufs_hba *hba,
 			  struct ufs_pa_layer_attr *pwr_mode)
 {
 	struct ufs_pa_layer_attr old_pwr_info;
+	unsigned int noio_flag;
 	int ret;
 
+	/*
+	 * ufshcd_tx_eqtr() is called from a power-mode-change context where
+	 * I/O is suspended. Use memalloc_noio_save() to propagate GFP_NOIO
+	 * to all allocations in the call tree instead of tagging each call
+	 * site individually.
+	 */
+	noio_flag = memalloc_noio_save();
+
 	if (!params->eqtr_record) {
 		params->eqtr_record = devm_kzalloc(hba->dev,
 						   sizeof(*params->eqtr_record),
 						   GFP_KERNEL);
-		if (!params->eqtr_record)
-			return -ENOMEM;
+		if (!params->eqtr_record) {
+			ret = -ENOMEM;
+			goto out_noio_restore;
+		}
 	}
 
 	memcpy(&old_pwr_info, &hba->pwr_info, sizeof(struct ufs_pa_layer_attr));
@@ -1244,6 +1256,9 @@ static int ufshcd_tx_eqtr(struct ufs_hba *hba,
 	if (ret)
 		ufshcd_tx_eqtr_unprepare(hba, &old_pwr_info);
 
+out_noio_restore:
+	memalloc_noio_restore(noio_flag);
+
 	return ret;
 }
 
-- 
2.34.1