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;
}
-
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