2006-08-26 16:35:40

by Oleg Nesterov

Subject: [PATCH RESEND] sys_ioprio_set: don't disable irqs

It is not good to disable interrupts while traversing all tasks in the system.
As I see it, sys_ioprio_get() doesn't need to do it at all, sys_ioprio_set()
does it for cfq_ioc_set_ioprio(), the latter can disable irqs itself.

Also, add a comment to explain why do we need tasklist_lock.

Signed-off-by: Oleg Nesterov <[email protected]>

--- 2.6.18-rc4/block/cfq-iosched.c~5_setpr 2006-08-27 00:37:03.000000000 +0400
+++ 2.6.18-rc4/block/cfq-iosched.c 2006-08-27 00:38:57.000000000 +0400
@@ -1421,14 +1421,14 @@ static inline void changed_ioprio(struct
}

/*
- * callback from sys_ioprio_set, irqs are disabled
+ * callback from sys_ioprio_set.
*/
static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
{
struct cfq_io_context *cic;
struct rb_node *n;

- spin_lock(&cfq_exit_lock);
+ spin_lock_irq(&cfq_exit_lock);

n = rb_first(&ioc->cic_root);
while (n != NULL) {
@@ -1438,7 +1438,7 @@ static int cfq_ioc_set_ioprio(struct io_
n = rb_next(n);
}

- spin_unlock(&cfq_exit_lock);
+ spin_unlock_irq(&cfq_exit_lock);

return 0;
}
--- 2.6.18-rc4/fs/ioprio.c~5_setpr 2006-08-27 00:37:03.000000000 +0400
+++ 2.6.18-rc4/fs/ioprio.c 2006-08-27 00:54:17.000000000 +0400
@@ -81,7 +81,12 @@ asmlinkage long sys_ioprio_set(int which
}

ret = -ESRCH;
- read_lock_irq(&tasklist_lock);
+ /*
+ * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
+ * so we can't use rcu_read_lock(). See re-copy of ->ioprio
+ * in copy_process().
+ */
+ read_lock(&tasklist_lock);
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
@@ -124,7 +129,7 @@ free_uid:
ret = -EINVAL;
}

- read_unlock_irq(&tasklist_lock);
+ read_unlock(&tasklist_lock);
return ret;
}

@@ -170,7 +175,7 @@ asmlinkage long sys_ioprio_get(int which
int ret = -ESRCH;
int tmpio;

- read_lock_irq(&tasklist_lock);
+ read_lock(&tasklist_lock);
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
@@ -221,7 +226,7 @@ asmlinkage long sys_ioprio_get(int which
ret = -EINVAL;
}

- read_unlock_irq(&tasklist_lock);
+ read_unlock(&tasklist_lock);
return ret;
}

2006-08-29 07:13:47

by Jens Axboe

Subject: Re: [PATCH RESEND] sys_ioprio_set: don't disable irqs

On Sun, Aug 27 2006, Oleg Nesterov wrote:
> It is not good to disable interrupts while traversing all tasks in the system.
> As I see it, sys_ioprio_get() doesn't need to do it at all, sys_ioprio_set()
> does it for cfq_ioc_set_ioprio(), the latter can disable irqs itself.
>
> Also, add a comment to explain why do we need tasklist_lock.
>
> Signed-off-by: Oleg Nesterov <[email protected]>

You should work against the 'block' branch in the block git repo, things
tend to change... I've applied your ioprio.c bit, the other one is not
needed anymore.

--
Jens Axboe