2007-11-03 00:35:30

by Mingming Cao

Subject: [PATCH][RFC]Ext4: Use get_cpu()/put_cpu() in preemptible context

Fix the warning of:

printk: 369 messages suppressed.
BUG: using smp_processor_id() in preemptible [00000001] code: fsx-linux/31702
caller is ext4_mb_new_blocks+0x2aa/0x1319

Signed-off-by: Mingming Cao <[email protected]>

---
fs/ext4/mballoc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
===================================================================
--- linux-2.6.24-rc1.orig/fs/ext4/mballoc.c 2007-11-02 17:22:18.000000000 -0700
+++ linux-2.6.24-rc1/fs/ext4/mballoc.c 2007-11-02 17:23:02.000000000 -0700
@@ -4006,7 +4006,8 @@ static void ext4_mb_group_or_file(struct
return;

BUG_ON(ac->ac_lg != NULL);
- ac->ac_lg = &sbi->s_locality_groups[smp_processor_id()];
+ ac->ac_lg = &sbi->s_locality_groups[get_cpu()];
+ put_cpu();

/* we're going to use group allocation */
ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;

2007-11-03 05:02:18

by Andreas Dilger

Subject: Re: [PATCH][RFC]Ext4: Use get_cpu()/put_cpu() in preemptible context

On Nov 02, 2007 17:35 -0700, Mingming Cao wrote:
> Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
> ===================================================================
> --- linux-2.6.24-rc1.orig/fs/ext4/mballoc.c 2007-11-02 17:22:18.000000000 -0700
> +++ linux-2.6.24-rc1/fs/ext4/mballoc.c 2007-11-02 17:23:02.000000000 -0700
> @@ -4006,7 +4006,8 @@ static void ext4_mb_group_or_file(struct
> return;
>
> BUG_ON(ac->ac_lg != NULL);
> - ac->ac_lg = &sbi->s_locality_groups[smp_processor_id()];
> + ac->ac_lg = &sbi->s_locality_groups[get_cpu()];
> + put_cpu();
>
> /* we're going to use group allocation */
> ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;

Shouldn't the put_cpu() be after ac->ac_lg is no longer being used?
I guess there would otherwise be a danger of other processes using
the same s_locality_groups[] struct?

Cheers, Andreas
--
Andreas Dilger
Sr. Software Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

2007-11-05 18:40:14

by Mingming Cao

Subject: Re: [PATCH][RFC]Ext4: Use get_cpu()/put_cpu() in preemptible context

On Sat, 2007-11-03 at 13:01 +0800, Andreas Dilger wrote:
> On Nov 02, 2007 17:35 -0700, Mingming Cao wrote:
> > Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
> > ===================================================================
> > --- linux-2.6.24-rc1.orig/fs/ext4/mballoc.c 2007-11-02 17:22:18.000000000 -0700
> > +++ linux-2.6.24-rc1/fs/ext4/mballoc.c 2007-11-02 17:23:02.000000000 -0700
> > @@ -4006,7 +4006,8 @@ static void ext4_mb_group_or_file(struct
> > return;
> >
> > BUG_ON(ac->ac_lg != NULL);
> > - ac->ac_lg = &sbi->s_locality_groups[smp_processor_id()];
> > + ac->ac_lg = &sbi->s_locality_groups[get_cpu()];
> > + put_cpu();
> >
> > /* we're going to use group allocation */
> > ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;
>
> Shouldn't the put_cpu() be after ac->ac_lg is no longer being used?
> I guess there would otherwise be a danger of other processes using
> the same s_locality_groups[] struct?

>From the code, the concurrent use of the same s_locality_groups is being
protected by the ac_lg->lg_sem. The put_cpu() instruction is before the
lock is taken.


Mingming