lib: percpu_counter_sub

Hugh spotted that some code does: percpu_counter_add(&counter, -unsignedlong) which, when the amount argument is of type s32, sort-of works thanks to two's-complement. However when we'd change the type to s64 this breaks on 32bit machines, because the promotion rules zero extend the unsigned number. Provide percpu_counter_sub() to hide the s64 cast. That is: percpu_counter_sub(&counter, foo) is equal to: percpu_counter_add(&counter, -(s64)foo); Signed-off-by: Peter Zijlstra <[email protected]> Cc: Hugh Dickins <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
ashr · Oct 17, 2007 · 3cb4f9f · 3cb4f9f
1 parent aa0dff2
commit 3cb4f9f
Show file tree

Hide file tree

Showing 4 changed files with 8 additions and 3 deletions.
diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
@@ -124,7 +124,7 @@ static int reserve_blocks(struct super_block *sb, int count)
 			return 0;
 	}
 
-	percpu_counter_add(&sbi->s_freeblocks_counter, -count);
+	percpu_counter_sub(&sbi->s_freeblocks_counter, count);
 	sb->s_dirt = 1;
 	return count;
 }

diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
@@ -1633,7 +1633,7 @@ ext3_fsblk_t ext3_new_blocks(handle_t *handle, struct inode *inode,
 	gdp->bg_free_blocks_count =
 			cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)-num);
 	spin_unlock(sb_bgl_lock(sbi, group_no));
-	percpu_counter_add(&sbi->s_freeblocks_counter, -num);
+	percpu_counter_sub(&sbi->s_freeblocks_counter, num);
 
 	BUFFER_TRACE(gdp_bh, "journal_dirty_metadata for group descriptor");
 	err = ext3_journal_dirty_metadata(handle, gdp_bh);

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
@@ -1647,7 +1647,7 @@ ext4_fsblk_t ext4_new_blocks(handle_t *handle, struct inode *inode,
 	gdp->bg_free_blocks_count =
 			cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)-num);
 	spin_unlock(sb_bgl_lock(sbi, group_no));
-	percpu_counter_add(&sbi->s_freeblocks_counter, -num);
+	percpu_counter_sub(&sbi->s_freeblocks_counter, num);
 
 	BUFFER_TRACE(gdp_bh, "journal_dirty_metadata for group descriptor");
 	err = ext4_journal_dirty_metadata(handle, gdp_bh);

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
@@ -105,4 +105,9 @@ static inline void percpu_counter_dec(struct percpu_counter *fbc)
 	percpu_counter_add(fbc, -1);
 }
 
+static inline void percpu_counter_sub(struct percpu_counter *fbc, s64 amount)
+{
+	percpu_counter_add(fbc, -amount);
+}
+
 #endif /* _LINUX_PERCPU_COUNTER_H */