[PATCH] fs: inode_set_flags() replace opencoded set_mask_bits()

[PATCH] fs: inode_set_flags() replace opencoded set_mask_bits()

[Vineet Gupta]

It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
introduced the set_mask_bits API, but somehow missed not using it in
ext4 in the end

Also, set_mask_bits is used in fs quite a bit and we can possibly come up
with a generic llsc based implementation (w/o the cmpxchg loop)

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 fs/inode.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index d30640f7a193..d892ff711615 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2005,13 +2005,7 @@ EXPORT_SYMBOL(inode_dio_wait);
 void inode_set_flags(struct inode *inode, unsigned int flags,
 		     unsigned int mask)
 {
-	unsigned int old_flags, new_flags;
-
 	WARN_ON_ONCE(flags & ~mask);
-	do {
-		old_flags = ACCESS_ONCE(inode->i_flags);
-		new_flags = (old_flags & ~mask) | flags;
-	} while (unlikely(cmpxchg(&inode->i_flags, old_flags,
-				  new_flags) != old_flags));
+	set_mask_bits(&inode->i_flags, mask, flags);
 }
 EXPORT_SYMBOL(inode_set_flags);
-- 
1.9.1

Re: [PATCH] fs: inode_set_flags() replace opencoded set_mask_bits()

[Peter Zijlstra]

On Fri, Aug 07, 2015 at 12:25:04PM +0530, Vineet Gupta wrote:
> It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
> ("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
> introduced the set_mask_bits API, but somehow missed not using it in
> ext4 in the end
> 
> Also, set_mask_bits is used in fs quite a bit and we can possibly come up
> with a generic llsc based implementation (w/o the cmpxchg loop)

May I also suggest changing the return value of set_mask_bits() to old.

You can compute the new value given old, but you cannot compute the old
value given new, therefore old is the better return value. Also, no
current user seems to use the return value, so changing it is without
risk.

Re: [PATCH] fs: inode_set_flags() replace opencoded set_mask_bits()

[Vineet Gupta]

On Friday 07 August 2015 04:40 PM, Peter Zijlstra wrote:
> On Fri, Aug 07, 2015 at 12:25:04PM +0530, Vineet Gupta wrote:
>> > It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
>> > ("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
>> > introduced the set_mask_bits API, but somehow missed not using it in
>> > ext4 in the end
>> > 
>> > Also, set_mask_bits is used in fs quite a bit and we can possibly come up
>> > with a generic llsc based implementation (w/o the cmpxchg loop)
> May I also suggest changing the return value of set_mask_bits() to old.
>
> You can compute the new value given old, but you cannot compute the old
> value given new, therefore old is the better return value. Also, no
> current user seems to use the return value, so changing it is without
> risk.

Makes sense - will do that early next week !