[PATCH 03/23] lib: percpu_counter_sub

From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: miklos@szeredi.hu, akpm@linux-foundation.org, neilb@suse.de,
	dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com,
	a.p.zijlstra@chello.nl, nikita@clusterfs.com,
	trond.myklebust@fys.uio.no, yingchao.zhou@gmail.com,
	richard@rsk.demon.co.uk, torvalds@linux-foundation.org,
	Hugh Dickins <hugh@veritas.com>
Subject: [PATCH 03/23] lib: percpu_counter_sub
Date: Tue, 11 Sep 2007 21:53:53 +0200	[thread overview]
Message-ID: <20070911200012.216056000@chello.nl> (raw)
In-Reply-To: 20070911195350.825778000@chello.nl

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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 <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hugh@veritas.com>
---
 fs/ext2/balloc.c               |    2 +-
 fs/ext3/balloc.c               |    2 +-
 fs/ext4/balloc.c               |    2 +-
 include/linux/percpu_counter.h |    5 +++++
 4 files changed, 8 insertions(+), 3 deletions(-)

Index: linux-2.6/fs/ext2/balloc.c
===================================================================

--- linux-2.6.orig/fs/ext2/balloc.c
+++ linux-2.6/fs/ext2/balloc.c
@@ -1367,7 +1367,7 @@ allocated:
 	}
 
 	group_adjust_blocks(sb, group_no, gdp, gdp_bh, -num);
-	percpu_counter_add(&sbi->s_freeblocks_counter, -num);
+	percpu_counter_sub(&sbi->s_freeblocks_counter, num);
 
 	mark_buffer_dirty(bitmap_bh);
 	if (sb->s_flags & MS_SYNCHRONOUS)
Index: linux-2.6/fs/ext3/balloc.c
===================================================================
--- linux-2.6.orig/fs/ext3/balloc.c
+++ linux-2.6/fs/ext3/balloc.c
@@ -1672,7 +1672,7 @@ 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);
Index: linux-2.6/fs/ext4/balloc.c
===================================================================
--- linux-2.6.orig/fs/ext4/balloc.c
+++ linux-2.6/fs/ext4/balloc.c
@@ -1697,7 +1697,7 @@ 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);
Index: linux-2.6/include/linux/percpu_counter.h
===================================================================
--- linux-2.6.orig/include/linux/percpu_counter.h
+++ linux-2.6/include/linux/percpu_counter.h
@@ -105,4 +105,9 @@ static inline void percpu_counter_dec(st
 	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 */

--

