copy_process:
// holds tasklist_lock + ->siglock
/*
* inherit ioprio
*/
p->ioprio = current->ioprio;
Why? ->ioprio was already copied in dup_task_struct(). I guess this is needed
to ensure that the child can't escape sys_ioprio_set(IOPRIO_WHO_{PGRP,USER}),
yes?
In that case we don't need ->siglock held, and the comment should be updated.
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.18-rc4/kernel/fork.c~1_fork 2006-08-19 17:50:56.000000000 +0400
+++ 2.6.18-rc4/kernel/fork.c 2006-08-20 18:18:47.000000000 +0400
@@ -1138,7 +1138,6 @@ static struct task_struct *copy_process(
/* Our parent execution domain becomes current domain
These must match for thread signalling to apply */
-
p->parent_exec_id = p->self_exec_id;
/* ok, now we should be set up.. */
@@ -1161,6 +1160,9 @@ static struct task_struct *copy_process(
/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);
+ /* for sys_ioprio_set(IOPRIO_WHO_PGRP) */
+ p->ioprio = current->ioprio;
+
/*
* The task hasn't been attached yet, so its cpus_allowed mask will
* not be changed, nor will its assigned CPU.
@@ -1220,11 +1222,6 @@ static struct task_struct *copy_process(
}
}
- /*
- * inherit ioprio
- */
- p->ioprio = current->ioprio;
-
if (likely(p->pid)) {
add_parent(p);
if (unlikely(p->ptrace & PT_PTRACED))
On Sun, 20 Aug 2006 18:53:21 +0400
Oleg Nesterov <[email protected]> wrote:
> copy_process:
> // holds tasklist_lock + ->siglock
> /*
> * inherit ioprio
> */
> p->ioprio = current->ioprio;
>
> Why? ->ioprio was already copied in dup_task_struct().
It might just be a thinko.
> I guess this is needed
> to ensure that the child can't escape sys_ioprio_set(IOPRIO_WHO_{PGRP,USER}),
> yes?
How could the child escape that if this assignment was not present?
> In that case we don't need ->siglock held, and the comment should be updated.
Surely.
On 08/21, Andrew Morton wrote:
>
> On Sun, 20 Aug 2006 18:53:21 +0400
> Oleg Nesterov <[email protected]> wrote:
>
> > copy_process:
> > // holds tasklist_lock + ->siglock
> > /*
> > * inherit ioprio
> > */
> > p->ioprio = current->ioprio;
> >
> > Why? ->ioprio was already copied in dup_task_struct().
>
> It might just be a thinko.
>
> > I guess this is needed
> > to ensure that the child can't escape sys_ioprio_set(IOPRIO_WHO_{PGRP,USER}),
> > yes?
>
> How could the child escape that if this assignment was not present?
It is possible that sys_ioprio_set(IOPRIO_WHO_PGRP) was called after
copy_process() already did dup_task_struct(), but before it takes
tasklist_lock. Documentation/block/ioprio.txt doesn't say should
ioprio_set() be "atomic" or not. If not, we can kill this line, and
(more importantly) drop tasklist_lock in fs/ioprio.c
Oleg.