linux-kernel - [PATCH 09/46] sched_ext: Add the @sch parameter to __bstr

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Message-ID: <20250920005931.2753828-10-tj@kernel.org>
Date: Fri, 19 Sep 2025 14:58:32 -1000
From: Tejun Heo <tj@...nel.org>
To: void@...ifault.com,
	arighi@...dia.com,
	multics69@...il.com
Cc: linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	memxor@...il.com,
	bpf@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 09/46] sched_ext: Add the @sch parameter to __bstr_format()

In preparation for multiple scheduler support, add the @sch parameter to
__bstr_format() and update the callers to read $scx_root, verify that it's
not NULL and pass it in. The passed in @sch parameter is not used yet.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/sched/ext.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 560ac5a575bd..373146154829 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6063,8 +6063,9 @@ __bpf_kfunc void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it)
 
 __bpf_kfunc_end_defs();
 
-static s32 __bstr_format(u64 *data_buf, char *line_buf, size_t line_size,
-			 char *fmt, unsigned long long *data, u32 data__sz)
+static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf,
+			 size_t line_size, char *fmt, unsigned long long *data,
+			 u32 data__sz)
 {
 	struct bpf_bprintf_data bprintf_data = { .get_bin_args = true };
 	s32 ret;
@@ -6099,10 +6100,10 @@ static s32 __bstr_format(u64 *data_buf, char *line_buf, size_t line_size,
 	return ret;
 }
 
-static s32 bstr_format(struct scx_bstr_buf *buf,
+static s32 bstr_format(struct scx_sched *sch, struct scx_bstr_buf *buf,
 		       char *fmt, unsigned long long *data, u32 data__sz)
 {
-	return __bstr_format(buf->data, buf->line, sizeof(buf->line),
+	return __bstr_format(sch, buf->data, buf->line, sizeof(buf->line),
 			     fmt, data, data__sz);
 }
 
@@ -6121,10 +6122,13 @@ __bpf_kfunc_start_defs();
 __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt,
 				   unsigned long long *data, u32 data__sz)
 {
+	struct scx_sched *sch;
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags);
-	if (bstr_format(&scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
+	sch = rcu_dereference_bh(scx_root);
+	if (likely(sch) &&
+	    bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
 		scx_kf_exit(SCX_EXIT_UNREG_BPF, exit_code, "%s", scx_exit_bstr_buf.line);
 	raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags);
 }
@@ -6141,10 +6145,13 @@ __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt,
 __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data,
 				    u32 data__sz)
 {
+	struct scx_sched *sch;
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags);
-	if (bstr_format(&scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
+	sch = rcu_dereference_bh(scx_root);
+	if (likely(sch) &&
+	    bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
 		scx_kf_exit(SCX_EXIT_ERROR_BPF, 0, "%s", scx_exit_bstr_buf.line);
 	raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags);
 }
@@ -6164,17 +6171,24 @@ __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data,
 __bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data,
 				   u32 data__sz)
 {
+	struct scx_sched *sch;
 	struct scx_dump_data *dd = &scx_dump_data;
 	struct scx_bstr_buf *buf = &dd->buf;
 	s32 ret;
 
+	guard(rcu)();
+
+	sch = rcu_dereference(scx_root);
+	if (unlikely(!sch))
+		return;
+
 	if (raw_smp_processor_id() != dd->cpu) {
 		scx_kf_error("scx_bpf_dump() must only be called from ops.dump() and friends");
 		return;
 	}
 
 	/* append the formatted string to the line buf */
-	ret = __bstr_format(buf->data, buf->line + dd->cursor,
+	ret = __bstr_format(sch, buf->data, buf->line + dd->cursor,
 			    sizeof(buf->line) - dd->cursor, fmt, data, data__sz);
 	if (ret < 0) {
 		dump_line(dd->s, "%s[!] (\"%s\", %p, %u) failed to format (%d)",
-- 
2.51.0