[PATCH] scsi: ufs: mediatek: Fix page faults in ufs_mtk_clk_scale trace event

[Keita Morisaki]

The ufs_mtk_clk_scale trace event currently stores the address of the
name string directly via __field(const char *, name). This pointer may
become invalid after the module is unloaded, causing page faults when
the trace buffer is subsequently accessed.

This can occur because the MediaTek UFS driver can be configured as a
loadable module (tristate in Kconfig), meaning the name string passed
to the trace event may reside in module memory that becomes invalid
after module unload.

Fix this by using __string() and __assign_str() to copy the string
contents into the ring buffer instead of storing the pointer. This
ensures the trace data remains valid regardless of module state.

This change increases the memory usage for each ftrace entry by a few
bytes (clock names are typically 7-15 characters like "ufs_sel" or
"ufs_sel_max_src") compared to storing an 8-byte pointer.

Note that this change does not affect anything unless all of the
following conditions are met:
- CONFIG_SCSI_UFS_MEDIATEK is enabled
- ftrace tracing is enabled
- The ufs_mtk_clk_scale event is enabled in ftrace

Signed-off-by: Keita Morisaki <keita.morisaki at tier4.jp>
---
 drivers/ufs/host/ufs-mediatek-trace.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/ufs/host/ufs-mediatek-trace.h b/drivers/ufs/host/ufs-mediatek-trace.h
index b5f2ec314..0df8ac843 100644
--- a/drivers/ufs/host/ufs-mediatek-trace.h
+++ b/drivers/ufs/host/ufs-mediatek-trace.h
@@ -33,19 +33,19 @@ TRACE_EVENT(ufs_mtk_clk_scale,
 	TP_ARGS(name, scale_up, clk_rate),
 
 	TP_STRUCT__entry(
-		__field(const char*, name)
+		__string(name, name)
 		__field(bool, scale_up)
 		__field(unsigned long, clk_rate)
 	),
 
 	TP_fast_assign(
-		__entry->name = name;
+		__assign_str(name);
 		__entry->scale_up = scale_up;
 		__entry->clk_rate = clk_rate;
 	),
 
 	TP_printk("ufs: clk (%s) scaled %s @ %lu",
-		  __entry->name,
+		  __get_str(name),
 		  __entry->scale_up ? "up" : "down",
 		  __entry->clk_rate)
 );

base-commit: 18f7fcd5e69a04df57b563360b88be72471d6b62
-- 
2.34.1