/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) <[email protected]> --- 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
