/proc/pressure/* are created when psi initializes and never removed.
Say so with PROC_ENTRY_PERMANENT, procfs then calls into them without
pinning them, like it does for /proc/profile.
That also takes care of a rule the files bent. psi_write() takes the
seq_file's lock to serialize the triggers. A reader holds that lock
while it copies to userspace, and now that procfs owns the seq_file it
does that with the entry unpinned. So nothing that runs with the entry
pinned may wait for that lock, and psi_write() ran pinned. Nothing ever
waited for it since the files are never removed, but with the files
permanent nothing runs pinned at all.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
kernel/sched/psi.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 3132105bf382..9811c3b705eb 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1622,6 +1622,7 @@ static int psi_fop_release(struct inode *inode, struct file *file)
}
static const struct proc_ops psi_io_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_show = psi_io_show,
.proc_write_buf = psi_io_write,
.proc_poll = psi_fop_poll,@@ -1629,6 +1630,7 @@ static const struct proc_ops psi_io_proc_ops = {
};
static const struct proc_ops psi_memory_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_show = psi_memory_show,
.proc_write_buf = psi_memory_write,
.proc_poll = psi_fop_poll,@@ -1636,6 +1638,7 @@ static const struct proc_ops psi_memory_proc_ops = {
};
static const struct proc_ops psi_cpu_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_show = psi_cpu_show,
.proc_write_buf = psi_cpu_write,
.proc_poll = psi_fop_poll,@@ -1655,6 +1658,7 @@ static ssize_t psi_irq_write(struct file *file, char *buf, size_t nbytes,
}
static const struct proc_ops psi_irq_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_show = psi_irq_show,
.proc_write_buf = psi_irq_write,
.proc_poll = psi_fop_poll,
--
2.53.0