Commit 3cb4f9fa authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aa0dff2d

fs/ext2/balloc.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

}

fs/ext3/balloc.c

+1 −1
Original line number Diff line number Diff line
@@ -1633,7 +1633,7 @@ allocated: 
	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);

fs/ext4/balloc.c

+1 −1
Original line number Diff line number Diff line
@@ -1647,7 +1647,7 @@ allocated: 
	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);

include/linux/percpu_counter.h

+5 −0
Original line number Diff line number Diff line
@@ -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 */

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