* Re: [PATCH 09/18] fs: rework icount to be a locked variable [not found] ` <1286515292-15882-10-git-send-email-david@fromorbit.com> @ 2010-10-08 7:27 ` Christoph Hellwig 2010-10-08 7:50 ` Dave Chinner 0 siblings, 1 reply; 4+ messages in thread From: Christoph Hellwig @ 2010-10-08 7:27 UTC (permalink / raw) To: Dave Chinner; +Cc: linux-fsdevel, linux-kernel, chris.mason, linux-btrfs > index 2953e9f..9f04478 100644 > --- a/fs/btrfs/inode.c > +++ b/fs/btrfs/inode.c > @@ -1964,8 +1964,14 @@ void btrfs_add_delayed_iput(struct inode *inode) > struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info; > struct delayed_iput *delayed; > > - if (atomic_add_unless(&inode->i_count, -1, 1)) > + /* XXX: filesystems should not play refcount games like this */ > + spin_lock(&inode->i_lock); > + if (inode->i_ref > 1) { > + inode->i_ref--; > + spin_unlock(&inode->i_lock); > return; > + } > + spin_unlock(&inode->i_lock); Yeah, all that i_count/i_ref mess in btrfs needs some serious work. Chris? > + > +/* > + * inode_lock must be held > + */ > +void iref_locked(struct inode *inode) > +{ > + inode->i_ref++; > +} > EXPORT_SYMBOL_GPL(iref_locked); I'm a big fan of _GPL exports, but adding this for a trivial counter increment seems a bit weird. > int iref_read(struct inode *inode) > { > - return atomic_read(&inode->i_count); > + int ref; > + > + spin_lock(&inode->i_lock); > + ref = inode->i_ref; > + spin_unlock(&inode->i_lock); > + return ref; > } There's no need to lock a normal 32-bit variable for readers. > + inode->i_ref--; > + if (inode->i_ref == 0) { if (--inode->i_ref == 0) { might be a bit more idiomatic. ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable 2010-10-08 7:27 ` [PATCH 09/18] fs: rework icount to be a locked variable Christoph Hellwig @ 2010-10-08 7:50 ` Dave Chinner 2010-10-08 8:17 ` Christoph Hellwig 0 siblings, 1 reply; 4+ messages in thread From: Dave Chinner @ 2010-10-08 7:50 UTC (permalink / raw) To: Christoph Hellwig; +Cc: linux-fsdevel, linux-kernel, chris.mason, linux-btrfs On Fri, Oct 08, 2010 at 03:27:49AM -0400, Christoph Hellwig wrote: > > index 2953e9f..9f04478 100644 > > --- a/fs/btrfs/inode.c > > +++ b/fs/btrfs/inode.c > > @@ -1964,8 +1964,14 @@ void btrfs_add_delayed_iput(struct inode *inode) > > struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info; > > struct delayed_iput *delayed; > > > > - if (atomic_add_unless(&inode->i_count, -1, 1)) > > + /* XXX: filesystems should not play refcount games like this */ > > + spin_lock(&inode->i_lock); > > + if (inode->i_ref > 1) { > > + inode->i_ref--; > > + spin_unlock(&inode->i_lock); > > return; > > + } > > + spin_unlock(&inode->i_lock); > > Yeah, all that i_count/i_ref mess in btrfs needs some serious work. > Chris? > > > + > > +/* > > + * inode_lock must be held > > + */ > > +void iref_locked(struct inode *inode) > > +{ > > + inode->i_ref++; > > +} > > EXPORT_SYMBOL_GPL(iref_locked); > > I'm a big fan of _GPL exports, but adding this for a trivial counter > increment seems a bit weird. OK, will drop the _GPL. > > > int iref_read(struct inode *inode) > > { > > - return atomic_read(&inode->i_count); > > + int ref; > > + > > + spin_lock(&inode->i_lock); > > + ref = inode->i_ref; > > + spin_unlock(&inode->i_lock); > > + return ref; > > } > > There's no need to lock a normal 32-bit variable for readers. Ok, but will need a memory barrier instead? > > > + inode->i_ref--; > > + if (inode->i_ref == 0) { > > if (--inode->i_ref == 0) { > > might be a bit more idiomatic. OK. Cheers, Dave. -- Dave Chinner david@fromorbit.com ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable 2010-10-08 7:50 ` Dave Chinner @ 2010-10-08 8:17 ` Christoph Hellwig 2010-10-08 13:16 ` Chris Mason 0 siblings, 1 reply; 4+ messages in thread From: Christoph Hellwig @ 2010-10-08 8:17 UTC (permalink / raw) To: Dave Chinner Cc: Christoph Hellwig, linux-fsdevel, linux-kernel, chris.mason, linux-btrfs On Fri, Oct 08, 2010 at 06:50:01PM +1100, Dave Chinner wrote: > > There's no need to lock a normal 32-bit variable for readers. > > Ok, but will need a memory barrier instead? Isn't spin_unlock supposed to be one? I'll need some of the locking experts to shime in. ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable 2010-10-08 8:17 ` Christoph Hellwig @ 2010-10-08 13:16 ` Chris Mason 0 siblings, 0 replies; 4+ messages in thread From: Chris Mason @ 2010-10-08 13:16 UTC (permalink / raw) To: Christoph Hellwig; +Cc: Dave Chinner, linux-fsdevel, linux-kernel, linux-btrfs On Fri, Oct 08, 2010 at 10:17:14AM +0200, Christoph Hellwig wrote: > On Fri, Oct 08, 2010 at 06:50:01PM +1100, Dave Chinner wrote: > > > There's no need to lock a normal 32-bit variable for readers. > > > > Ok, but will need a memory barrier instead? > > Isn't spin_unlock supposed to be one? I'll need some of the locking > experts to shime in. Not really a locking expert, but the locking operations are supposed to have an implicit barrier. -chris ^ permalink raw reply [flat|nested] 4+ messages in thread
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[not found] ` <1286515292-15882-10-git-send-email-david@fromorbit.com>
2010-10-08 7:27 ` [PATCH 09/18] fs: rework icount to be a locked variable Christoph Hellwig
2010-10-08 7:50 ` Dave Chinner
2010-10-08 8:17 ` Christoph Hellwig
2010-10-08 13:16 ` Chris Mason
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