[PATCH 25/28] EDAC/thunderx: Replace strlcat() with seq_buf

The threaded ISR handlers (thunderx_ocx_com_threaded_isr(),
thunderx_ocx_lnk_threaded_isr(), and thunderx_l2c_threaded_isr()) build
multi-line error reports by formatting register details into a scratch
buffer and appending them to "msg" with strlcat().

In preparation for removing the deprecated strlcat() API[1], refactor the
ISR handlers to construct error messages using struct seq_buf.

Additionally, fix two bugs in decode_register(): initialize "str[0] = '\0'"
so callers do not append stale buffer contents when no error bits match,
and stop iterating if snprintf() truncates the buffer to avoid
underflowing the remaining "size" counter.

Link: https://github.com/KSPP/linux/issues/370 [1]
Cc: codemender-patching+linux@google.com
Assisted-by: AI:Claude-3-5-Sonnet [editor_update_file, shell_command_run]
Signed-off-by: Bill Wendling <morbo@google.com>
---
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---
 drivers/edac/thunderx_edac.c | 64 ++++++++++++++++++++++--------------
 1 file changed, 39 insertions(+), 25 deletions(-)

diff --git a/drivers/edac/thunderx_edac.c b/drivers/edac/thunderx_edac.c
index e7c335ca0c36..4e3781815b6d 100644
--- a/drivers/edac/thunderx_edac.c
+++ b/drivers/edac/thunderx_edac.c

@@ -20,6 +20,7 @@
 #include <linux/atomic.h>
 #include <linux/bitfield.h>
 #include <linux/circ_buf.h>
+#include <linux/seq_buf.h>
 
 #include <asm/page.h>
 

@@ -47,12 +48,17 @@ static void decode_register(char *str, size_t size,
 {
 	int ret = 0;
 
+	if (size > 0)
+		str[0] = '\0';
+
 	while (descr->type && descr->mask && descr->descr) {
 		if (reg & descr->mask) {
 			ret = snprintf(str, size, "\n\t%s, %s",
 				       descr->type == ERR_CORRECTED ?
 					 "Corrected" : "Uncorrected",
 				       descr->descr);
+			if (ret < 0 || ret >= size)
+				break;
 			str += ret;
 			size -= ret;
 		}

@@ -1115,35 +1121,37 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
 
 	while (CIRC_CNT(ocx->com_ring_head, ocx->com_ring_tail,
 			ARRAY_SIZE(ocx->com_err_ctx))) {
+		struct seq_buf s;
+
 		tail = ring_pos(ocx->com_ring_tail,
 				ARRAY_SIZE(ocx->com_err_ctx));
 		ctx = &ocx->com_err_ctx[tail];
 
-		snprintf(msg, OCX_MESSAGE_SIZE, "%s: OCX_COM_INT: %016llx",
-			ocx->edac_dev->ctl_name, ctx->reg_com_int);
+		seq_buf_init(&s, msg, OCX_MESSAGE_SIZE);
+
+		seq_buf_printf(&s, "%s: OCX_COM_INT: %016llx",
+			       ocx->edac_dev->ctl_name, ctx->reg_com_int);
 
 		decode_register(other, OCX_OTHER_SIZE,
 				ocx_com_errors, ctx->reg_com_int);
 
-		strlcat(msg, other, OCX_MESSAGE_SIZE);
+		seq_buf_puts(&s, other);
 
 		for (lane = 0; lane < OCX_RX_LANES; lane++)
 			if (ctx->reg_com_int & BIT(lane)) {
-				snprintf(other, OCX_OTHER_SIZE,
-					 "\n\tOCX_LNE_INT[%02d]: %016llx OCX_LNE_STAT11[%02d]: %016llx",
-					 lane, ctx->reg_lane_int[lane],
-					 lane, ctx->reg_lane_stat11[lane]);
-
-				strlcat(msg, other, OCX_MESSAGE_SIZE);
+				seq_buf_printf(&s,
+					       "\n\tOCX_LNE_INT[%02d]: %016llx OCX_LNE_STAT11[%02d]: %016llx",
+					       lane, ctx->reg_lane_int[lane],
+					       lane, ctx->reg_lane_stat11[lane]);
 
 				decode_register(other, OCX_OTHER_SIZE,
 						ocx_lane_errors,
 						ctx->reg_lane_int[lane]);
-				strlcat(msg, other, OCX_MESSAGE_SIZE);
+				seq_buf_puts(&s, other);
 			}
 
 		if (ctx->reg_com_int & OCX_COM_INT_CE)
-			edac_device_handle_ce(ocx->edac_dev, 0, 0, msg);
+			edac_device_handle_ce(ocx->edac_dev, 0, 0, seq_buf_str(&s));
 
 		ocx->com_ring_tail++;
 	}

@@ -1196,25 +1204,28 @@ static irqreturn_t thunderx_ocx_lnk_threaded_isr(int irq, void *irq_id)
 
 	while (CIRC_CNT(ocx->link_ring_head, ocx->link_ring_tail,
 			ARRAY_SIZE(ocx->link_err_ctx))) {
+		struct seq_buf s;
+
 		tail = ring_pos(ocx->link_ring_head,
 				ARRAY_SIZE(ocx->link_err_ctx));
 
 		ctx = &ocx->link_err_ctx[tail];
 
-		snprintf(msg, OCX_MESSAGE_SIZE,
-			 "%s: OCX_COM_LINK_INT[%d]: %016llx",
-			 ocx->edac_dev->ctl_name,
-			 ctx->link, ctx->reg_com_link_int);
+		seq_buf_init(&s, msg, OCX_MESSAGE_SIZE);
+
+		seq_buf_printf(&s, "%s: OCX_COM_LINK_INT[%d]: %016llx",
+			       ocx->edac_dev->ctl_name,
+			       ctx->link, ctx->reg_com_link_int);
 
 		decode_register(other, OCX_OTHER_SIZE,
 				ocx_com_link_errors, ctx->reg_com_link_int);
 
-		strlcat(msg, other, OCX_MESSAGE_SIZE);
+		seq_buf_puts(&s, other);
 
 		if (ctx->reg_com_link_int & OCX_COM_LINK_INT_UE)
-			edac_device_handle_ue(ocx->edac_dev, 0, 0, msg);
+			edac_device_handle_ue(ocx->edac_dev, 0, 0, seq_buf_str(&s));
 		else if (ctx->reg_com_link_int & OCX_COM_LINK_INT_CE)
-			edac_device_handle_ce(ocx->edac_dev, 0, 0, msg);
+			edac_device_handle_ce(ocx->edac_dev, 0, 0, seq_buf_str(&s));
 
 		ocx->link_ring_tail++;
 	}

@@ -1880,22 +1891,25 @@ static irqreturn_t thunderx_l2c_threaded_isr(int irq, void *irq_id)
 
 	while (CIRC_CNT(l2c->ring_head, l2c->ring_tail,
 			ARRAY_SIZE(l2c->err_ctx))) {
+		struct seq_buf s;
+
 		tail = ring_pos(l2c->ring_tail, ARRAY_SIZE(l2c->err_ctx));
 		ctx = &l2c->err_ctx[tail];
 
-		snprintf(msg, L2C_MESSAGE_SIZE,
-			 "%s: %s: %016llx, %s: %016llx",
-			 l2c->edac_dev->ctl_name, reg_int_name, ctx->reg_int,
-			 ctx->reg_ext_name, ctx->reg_ext);
+		seq_buf_init(&s, msg, L2C_MESSAGE_SIZE);
+
+		seq_buf_printf(&s, "%s: %s: %016llx, %s: %016llx",
+			       l2c->edac_dev->ctl_name, reg_int_name, ctx->reg_int,
+			       ctx->reg_ext_name, ctx->reg_ext);
 
 		decode_register(other, L2C_OTHER_SIZE, l2_errors, ctx->reg_int);
 
-		strlcat(msg, other, L2C_MESSAGE_SIZE);
+		seq_buf_puts(&s, other);
 
 		if (ctx->reg_int & mask_ue)
-			edac_device_handle_ue(l2c->edac_dev, 0, 0, msg);
+			edac_device_handle_ue(l2c->edac_dev, 0, 0, seq_buf_str(&s));
 		else if (ctx->reg_int & mask_ce)
-			edac_device_handle_ce(l2c->edac_dev, 0, 0, msg);
+			edac_device_handle_ce(l2c->edac_dev, 0, 0, seq_buf_str(&s));
 
 		l2c->ring_tail++;
 	}

-- 
2.55.0.1032.g73a4cd73de-goog