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Ext4: Use get_cpu()/put_cpu() in preemptible context

RFC PATCH In review Mingming Cao 2 participants 3 messages Nov 3, 2007 – Nov 5, 2007 3 messages not in the archive ext4 file system

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A message that is not in the archive (sent off-list or not yet received): E1Inx4A-0002PQ-00@kernel

A message that is not in the archive (sent off-list or not yet received): [email protected]

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Mingming Cao

author
#3 lore raw

RFC PATCH 1/1 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(-)
fs/ext4/mballoc.c +2 -1
Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
===================================================================
@@ -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;
#4 lore raw
Quoted 5 lines · Mingming Cao

Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
===================================================================

fs/ext4/mballoc.c static void ext4_mb_group_or_file(struct · line 4013

Quoted 9 lines
fs/ext4/mballoc.c +2 -1
@@ -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.

author
#5 lore raw
Quoted 13 lines · Andreas Dilger
Quoted 12 lines · Mingming Cao

Index: linux-2.6.24-rc1/fs/ext4/mballoc.c
===================================================================

fs/ext4/mballoc.c +2 -1
@@ -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();
Quoted 8 lines

fs/ext4/mballoc.c static void ext4_mb_group_or_file(struct · line 4013

Quoted 2 lines
fs/ext4/mballoc.c +0 -0
 	/* 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