[PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[Ian Bridges]

In preparation for removing the strlcat() API[1], replace its uses in
the error message construction of the ThunderX OCX and L2C threaded
IRQ handlers.

The OCX link and L2C handlers append a single decoded-register string,
so the whole message can be produced with one snprintf(). The OCX com
handler accumulates a variable number of fragments in a per-lane loop,
so use a struct seq_buf, which tracks the current write position and
remaining space internally. seq_buf_str() keeps the message
NUL-terminated for edac_device_handle_ce().

Link: https://github.com/KSPP/linux/issues/370 [1]
Signed-off-by: Ian Bridges <icb@fastmail.org>
---
The seq_buf conversion introduces one behavioral difference on
overflow. strlcat() copied as much of a fragment as would fit, but
seq_buf_puts() is all-or-nothing. A message longer than
OCX_MESSAGE_SIZE therefore truncates at a fragment boundary instead of
mid-fragment. The message was truncated either way.

I don't have ThunderX hardware, so I tested the patch with:
 - arm64 cross-build at W=1 with no warnings. Applies cleanly on
   v7.2-rc1.
 - Module load/unload in an arm64 QEMU guest.
 - A userspace harness comparing old and new message construction;
   outputs matched across ~500k register patterns.

 drivers/edac/thunderx_edac.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/edac/thunderx_edac.c b/drivers/edac/thunderx_edac.c
index 75c04dfc3962..5210ca18473d 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>
 
@@ -1108,6 +1109,7 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
 	int lane;
 	char *msg;
 	char *other;
+	struct seq_buf sb;
 
 	msg = kmalloc(OCX_MESSAGE_SIZE, GFP_KERNEL);
 	other = kmalloc(OCX_OTHER_SIZE, GFP_KERNEL);
@@ -1121,13 +1123,14 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
 				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(&sb, msg, OCX_MESSAGE_SIZE);
+		seq_buf_printf(&sb, "%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(&sb, other);
 
 		for (lane = 0; lane < OCX_RX_LANES; lane++)
 			if (ctx->reg_com_int & BIT(lane)) {
@@ -1136,16 +1139,17 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
 					 lane, ctx->reg_lane_int[lane],
 					 lane, ctx->reg_lane_stat11[lane]);
 
-				strlcat(msg, other, OCX_MESSAGE_SIZE);
+				seq_buf_puts(&sb, other);
 
 				decode_register(other, OCX_OTHER_SIZE,
 						ocx_lane_errors,
 						ctx->reg_lane_int[lane]);
-				strlcat(msg, other, OCX_MESSAGE_SIZE);
+				seq_buf_puts(&sb, 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(&sb));
 
 		ocx->com_ring_tail++;
 	}
@@ -1203,15 +1207,13 @@ static irqreturn_t thunderx_ocx_lnk_threaded_isr(int irq, void *irq_id)
 
 		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);
-
 		decode_register(other, OCX_OTHER_SIZE,
 				ocx_com_link_errors, ctx->reg_com_link_int);
 
-		strlcat(msg, other, OCX_MESSAGE_SIZE);
+		snprintf(msg, OCX_MESSAGE_SIZE,
+			 "%s: OCX_COM_LINK_INT[%d]: %016llx%s",
+			 ocx->edac_dev->ctl_name,
+			 ctx->link, ctx->reg_com_link_int, other);
 
 		if (ctx->reg_com_link_int & OCX_COM_LINK_INT_UE)
 			edac_device_handle_ue(ocx->edac_dev, 0, 0, msg);
@@ -1882,14 +1884,12 @@ 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))) {
-		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);
-
 		decode_register(other, L2C_OTHER_SIZE, l2_errors, ctx->reg_int);
 
-		strlcat(msg, other, L2C_MESSAGE_SIZE);
+		snprintf(msg, L2C_MESSAGE_SIZE,
+			 "%s: %s: %016llx, %s: %016llx%s",
+			 l2c->edac_dev->ctl_name, reg_int_name, ctx->reg_int,
+			 ctx->reg_ext_name, ctx->reg_ext, other);
 
 		if (ctx->reg_int & mask_ue)
 			edac_device_handle_ue(l2c->edac_dev, 0, 0, msg);
-- 
2.47.3

Re: [PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[Ian Bridges]

On Thu, Jul 02, 2026 at 01:46:45AM -0500, Ian Bridges wrote:

Gentle ping. This patch has had no response since it was posted on
July 2. The code it converts is unchanged on ras.git edac-for-next
as of this week, and the patch still applies cleanly. Happy to
resend if that is easier.

Thanks,
Ian

Re: [PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[Borislav Petkov]

On Wed, Jul 29, 2026 at 03:57:14PM -0500, Ian Bridges wrote:
> On Thu, Jul 02, 2026 at 01:46:45AM -0500, Ian Bridges wrote:
> Gentle ping. This patch has had no response since it was posted on
> July 2. The code it converts is unchanged on ras.git edac-for-next
> as of this week, and the patch still applies cleanly. Happy to
> resend if that is easier.

Are you in a hurry with this or is there anything that needs immediate
handling?

And I obviously can't apply untested patches.

Also, I see you've CCed the maintainer of that driver so he should probably
take a look.

And talking about maintainers, Sashiko points out a bunch of previous issues
with this driver:

https://sashiko.dev/#/patchset/akYJUdY1hVABUQH6%40dev

so, Robert, what's the story here, are we still caring for this or can I mark
it obsolete and drop it?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[Ian Bridges]

On Wed, Jul 29, 2026 at 04:00:35PM -0700, Borislav Petkov wrote:
> Are you in a hurry with this or is there anything that needs immediate
> handling?

No, there is no hurry on my end. I'm still new to this process, so if
the ping was not appropriate here please let me know.

Thanks,
Ian

Re: [PATCH] EDAC/thunderx: Replace strlcat() with snprintf() and seq_buf

[Borislav Petkov]

On Wed, Jul 29, 2026 at 09:35:38PM -0500, Ian Bridges wrote:
> On Wed, Jul 29, 2026 at 04:00:35PM -0700, Borislav Petkov wrote:
> No, there is no hurry on my end. I'm still new to this process, so if
> the ping was not appropriate here please let me know.

Nah, the ping is ok. But soon you'll realize that everyone is overloaded with
work.

If you're wondering how to best help out, reviewing and testing patches is
very welcome.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette