Hi Dan,
Thanks for the review,
On Tue, May 17, 2016 at 12:34:57PM -0700, Dan Williams wrote:
> On Tue, May 17, 2016 at 11:29 AM, Jon Derrick
> <jonathan.derrick@xxxxxxxxx> wrote:
> > This patch fixes S_DAX bd_inode i_flag locking to conform to suggested
>
> A "fix" implies that its currently broken. I don't see how it is, not
> until we add an ioctl method or other path that also tries to update
> the flags outside of blkdev_get() context. So, I don't think this
> patch stands on its own if you were intending it to be merged
> separately.
Are there no other paths that can set/clear a bd_inode->i_flags?
If not, that's fine and I'll pack this into the next HIPRI set
>
> > locking rules. It is presumed that S_DAX is the only valid inode flag
> > for a block device which subscribes to direct-access, and will restore
> > any previously set flags if direct-access initialization fails.
> >
> > This reverts to i_flags behavior prior to
> > bbab37ddc20bae4709bca8745c128c4f46fe63c5
> > by allowing other bd_inode flags when DAX is disabled
> >
> > Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> > ---
> > fs/block_dev.c | 31 ++++++++++++++++++++++++++-----
> > 1 file changed, 26 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/block_dev.c b/fs/block_dev.c
> > index 20a2c02..d41e37f 100644
> > --- a/fs/block_dev.c
> > +++ b/fs/block_dev.c
> > @@ -1159,6 +1159,20 @@ void bd_set_size(struct block_device *bdev, loff_t size)
> > }
> > EXPORT_SYMBOL(bd_set_size);
> >
> > +static void bd_add_dax(struct inode *inode)
> > +{
> > + inode_lock(inode);
> > + inode->i_flags |= S_DAX;
> > + inode_unlock(inode);
> > +}
> > +
> > +static void bd_clear_dax(struct inode *inode)
> > +{
> > + inode_lock(inode);
> > + inode->i_flags &= ~S_DAX;
> > + inode_unlock(inode);
> > +}
>
> Since this is inode generic should these helpers be prefixed "i_"
> rather than "bd_"?
That's fine. bd_acquire/forget also use the inode in its parameter list, but its simple enough to use the bdev instead for these functions or i_ as you suggest
>
> > +
> > static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part);
> >
> > /*
> > @@ -1172,6 +1186,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > {
> > struct gendisk *disk;
> > struct module *owner;
> > + struct inode *inode;
> > int ret;
> > int partno;
> > int perm = 0;
> > @@ -1198,6 +1213,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > if (!disk)
> > goto out;
> > owner = disk->fops->owner;
> > + inode = bdev->bd_inode;
> >
> > disk_block_events(disk);
> > mutex_lock_nested(&bdev->bd_mutex, for_part);
> > @@ -1206,9 +1222,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > bdev->bd_queue = disk->queue;
> > bdev->bd_contains = bdev;
> > if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops->direct_access)
> > - bdev->bd_inode->i_flags = S_DAX;
> > - else
> > - bdev->bd_inode->i_flags = 0;
> > + bd_add_dax(inode);
> >
> > if (!partno) {
> > ret = -ENXIO;
> > @@ -1228,6 +1242,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > bdev->bd_part = NULL;
> > bdev->bd_disk = NULL;
> > bdev->bd_queue = NULL;
> > + bd_clear_dax(inode);
> > mutex_unlock(&bdev->bd_mutex);
> > disk_unblock_events(disk);
> > put_disk(disk);
> > @@ -1239,7 +1254,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > if (!ret) {
> > bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
> > if (!blkdev_dax_capable(bdev))
> > - bdev->bd_inode->i_flags &= ~S_DAX;
> > + bd_clear_dax(inode);
> > }
> >
> > /*
> > @@ -1276,7 +1291,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > }
> > bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
> > if (!blkdev_dax_capable(bdev))
> > - bdev->bd_inode->i_flags &= ~S_DAX;
> > + bd_clear_dax(inode);
> > }
> > } else {
> > if (bdev->bd_contains == bdev) {
> > @@ -1297,6 +1312,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > put_disk(disk);
> > module_put(owner);
> > }
> > + inode_lock(inode);
> > + if (inode->i_flags & S_DAX)
> > + inode->i_flags = S_DAX;
> > + inode_unlock(inode);
> > +
>
> Clear all other flags if S_DAX is set? Why?
Code today sets i_flags = S_DAX, clearing all other flags, so I figured that's how it's supposed to be. Though I can't see any reason it has to be that way.
>
> > bdev->bd_openers++;
> > if (for_part)
> > bdev->bd_part_count++;
> > @@ -1309,6 +1329,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> > bdev->bd_disk = NULL;
> > bdev->bd_part = NULL;
> > bdev->bd_queue = NULL;
> > + bd_clear_dax(inode);
>
> Why?
As far as I can tell, this path is only for cleanup when a whole block device or partition block device fails to get. Your question makes me think I don't understand this part of the code correctly, and admittedly I don't understand it all that well.
All callers of out_clear set an error code on ret, so I assumed all instances of out_clear are errors. There's no reason to keep the S_DAX flag on the bdev this time around. If it resolves itself (for example, GENHD_FL_UP gets set), it can be set again on the next __blkdev_get pass.
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