[PATCH v2] pstore/zone: Emit registration message as a single pr_info()

[Kartik Rajput <kkartik@nvidia.com>]

register_pstore_zone() prints its "registered ... as backend for ..."
summary as a pr_info() followed by several pr_cont() calls.

pr_cont() is not atomic and has no log level of its own. It appends
to whichever line was most recently opened by a printk(). If a
pr_err() or pr_warn() from another CPU or an interrupt handler
preempts the pr_info() / pr_cont() sequence, it closes the
continuation between the fragments. This can cause parts of the
pstore registration message to appear at the wrong log level and be
interleaved with other messages.

Furthermore, this causes the detection of new warning and error
messages in the kernel log to be unreliable.

Format the registration line into a seq_buf and emit it with a
single pr_info() call, making the line atomic with respect to
concurrent printk() callers.  No functional change to registration.

Signed-off-by: Kartik Rajput <kkartik@nvidia.com>
---
Changes in v2:
- Use a seq_buf to build the registration line instead of scnprintf()
  calls.
- Link to v1: https://lore.kernel.org/all/20260424095820.1433700-1-kkartik@nvidia.com/
---
 fs/pstore/zone.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/pstore/zone.c b/fs/pstore/zone.c
index a3b003f9a3a0..004a5d5f376b 100644
--- a/fs/pstore/zone.c
+++ b/fs/pstore/zone.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/mount.h>
 #include <linux/printk.h>
+#include <linux/seq_buf.h>
 #include <linux/fs.h>
 #include <linux/pstore_zone.h>
 #include <linux/kdev_t.h>
@@ -1301,6 +1302,10 @@ int register_pstore_zone(struct pstore_zone_info *info)
 {
 	int err = -EINVAL;
 	struct psz_context *cxt = &pstore_zone_cxt;
+	char buf[256];
+	struct seq_buf s;
+
+	seq_buf_init(&s, buf, sizeof(buf));
 
 	if (info->total_size < 4096) {
 		pr_warn("total_size must be >= 4096\n");
@@ -1383,30 +1388,28 @@ int register_pstore_zone(struct pstore_zone_info *info)
 	}
 	cxt->pstore.data = cxt;
 
-	pr_info("registered %s as backend for", info->name);
 	cxt->pstore.max_reason = info->max_reason;
 	cxt->pstore.name = info->name;
 	if (info->kmsg_size) {
 		cxt->pstore.flags |= PSTORE_FLAGS_DMESG;
-		pr_cont(" kmsg(%s",
-			kmsg_dump_reason_str(cxt->pstore.max_reason));
-		if (cxt->pstore_zone_info->panic_write)
-			pr_cont(",panic_write");
-		pr_cont(")");
+		seq_buf_printf(&s, " kmsg(%s%s)",
+			       kmsg_dump_reason_str(cxt->pstore.max_reason),
+			       cxt->pstore_zone_info->panic_write ? ",panic_write" : "");
 	}
 	if (info->pmsg_size) {
 		cxt->pstore.flags |= PSTORE_FLAGS_PMSG;
-		pr_cont(" pmsg");
+		seq_buf_puts(&s, " pmsg");
 	}
 	if (info->console_size) {
 		cxt->pstore.flags |= PSTORE_FLAGS_CONSOLE;
-		pr_cont(" console");
+		seq_buf_puts(&s, " console");
 	}
 	if (info->ftrace_size) {
 		cxt->pstore.flags |= PSTORE_FLAGS_FTRACE;
-		pr_cont(" ftrace");
+		seq_buf_puts(&s, " ftrace");
 	}
-	pr_cont("\n");
+
+	pr_info("registered %s as backend for%s\n", info->name, seq_buf_str(&s));
 
 	err = pstore_register(&cxt->pstore);
 	if (err) {
-- 
2.43.0