Hello Christoph,
On Fri, Oct 11, 2024 at 01:24:15AM -0700, Christoph Hellwig wrote:
> On Thu, Oct 10, 2024 at 07:15:08AM -0700, Breno Leitao wrote:
> > Whenever an I/O elevator is changed, the system attempts to load a
> > module for the new elevator. This occurs regardless of whether the
> > elevator is already loaded or built directly into the kernel. This
> > behavior introduces unnecessary overhead and potential issues.
> >
> > This makes the operation slower, and more error-prone. For instance,
> > making the problem fixed by [1] visible for users that doesn't even rely
> > on modules being available through modules.
> >
> > Do not try to load the ioscheduler if it is already visible.
> >
> > This change brings two main benefits: it improves the performance of
> > elevator changes, and it reduces the likelihood of errors occurring
> > during this process.
> >
> > [1] Commit e3accac1a976 ("block: Fix elv_iosched_local_module handling of "none" scheduler")
> > Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> > ---
> > block/elevator.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/elevator.c b/block/elevator.c
> > index 4122026b11f1..1904e217505a 100644
> > --- a/block/elevator.c
> > +++ b/block/elevator.c
> > @@ -709,13 +709,16 @@ int elv_iosched_load_module(struct gendisk *disk, const char *buf,
> > size_t count)
> > {
> > char elevator_name[ELV_NAME_MAX];
> > + const char *name;
> >
> > if (!elv_support_iosched(disk->queue))
> > return -EOPNOTSUPP;
> >
> > strscpy(elevator_name, buf, sizeof(elevator_name));
> > + name = strstrip(elevator_name);
> >
> > - request_module("%s-iosched", strstrip(elevator_name));
> > + if (!__elevator_find(name))
>
> __elevator_find needs to be called with elv_list_lock.
That is right. Thanks for the heads-up.
I will send a fix soon.
