# \[PATCH RFC 17/27\] sched/psi: let procfs copy in trigger writes

- From: Christian Brauner \<brauner@kernel.org\>
- Date: 2026-11-02 15:25:51 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/11/17845562
- Thread: https://ratatoskr.run/linux-fsdevel/2026/11/17844895/t/2.md

```text
Implement ->proc_write_buf() for the files in /proc/pressure so procfs
copies in what is written before it pins the entry, and take the
trigger from that copy. Only the first 31 bytes were ever looked at.
Writes larger than PAGE_SIZE - 1 bytes fail with -EINVAL now.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 kernel/sched/psi.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index bcb8bf4e0b69..3132105bf382 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1535,8 +1535,8 @@ static int psi_cpu_show(struct seq_file *m, void *v)
 	return psi_show(m, &psi_system, PSI_CPU);
 }
 
-static ssize_t psi_write(struct file *file, const char __user *user_buf,
-			 size_t nbytes, enum psi_res res)
+static ssize_t psi_write(struct file *file, const char *kbuf, size_t nbytes,
+			 enum psi_res res)
 {
 	char buf[32];
 	size_t buf_size;
@@ -1552,9 +1552,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
 		return -EINVAL;
 
 	buf_size = min(nbytes, sizeof(buf));
-	if (copy_from_user(buf, user_buf, buf_size))
-		return -EFAULT;
-
+	memcpy(buf, kbuf, buf_size);
 	buf[buf_size - 1] = '\0';
 
 	seq = file->private_data;
@@ -1590,22 +1588,22 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
 	return nbytes;
 }
 
-static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
-			    size_t nbytes, loff_t *ppos)
+static ssize_t psi_io_write(struct file *file, char *buf, size_t nbytes,
+			    loff_t *ppos)
 {
-	return psi_write(file, user_buf, nbytes, PSI_IO);
+	return psi_write(file, buf, nbytes, PSI_IO);
 }
 
-static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
-				size_t nbytes, loff_t *ppos)
+static ssize_t psi_memory_write(struct file *file, char *buf, size_t nbytes,
+				loff_t *ppos)
 {
-	return psi_write(file, user_buf, nbytes, PSI_MEM);
+	return psi_write(file, buf, nbytes, PSI_MEM);
 }
 
-static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
-			     size_t nbytes, loff_t *ppos)
+static ssize_t psi_cpu_write(struct file *file, char *buf, size_t nbytes,
+			     loff_t *ppos)
 {
-	return psi_write(file, user_buf, nbytes, PSI_CPU);
+	return psi_write(file, buf, nbytes, PSI_CPU);
 }
 
 static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
@@ -1625,21 +1623,21 @@ static int psi_fop_release(struct inode *inode, struct file *file)
 
 static const struct proc_ops psi_io_proc_ops = {
 	.proc_show	= psi_io_show,
-	.proc_write	= psi_io_write,
+	.proc_write_buf	= psi_io_write,
 	.proc_poll	= psi_fop_poll,
 	.proc_release	= psi_fop_release,
 };
 
 static const struct proc_ops psi_memory_proc_ops = {
 	.proc_show	= psi_memory_show,
-	.proc_write	= psi_memory_write,
+	.proc_write_buf	= psi_memory_write,
 	.proc_poll	= psi_fop_poll,
 	.proc_release	= psi_fop_release,
 };
 
 static const struct proc_ops psi_cpu_proc_ops = {
 	.proc_show	= psi_cpu_show,
-	.proc_write	= psi_cpu_write,
+	.proc_write_buf	= psi_cpu_write,
 	.proc_poll	= psi_fop_poll,
 	.proc_release	= psi_fop_release,
 };
@@ -1650,15 +1648,15 @@ static int psi_irq_show(struct seq_file *m, void *v)
 	return psi_show(m, &psi_system, PSI_IRQ);
 }
 
-static ssize_t psi_irq_write(struct file *file, const char __user *user_buf,
-			     size_t nbytes, loff_t *ppos)
+static ssize_t psi_irq_write(struct file *file, char *buf, size_t nbytes,
+			     loff_t *ppos)
 {
-	return psi_write(file, user_buf, nbytes, PSI_IRQ);
+	return psi_write(file, buf, nbytes, PSI_IRQ);
 }
 
 static const struct proc_ops psi_irq_proc_ops = {
 	.proc_show	= psi_irq_show,
-	.proc_write	= psi_irq_write,
+	.proc_write_buf	= psi_irq_write,
 	.proc_poll	= psi_fop_poll,
 	.proc_release	= psi_fop_release,
 };

-- 
2.53.0

```