Re: [PATCH V4 09/13] fs/xfs: Add write aops lock to xfs layer

From: Ira Weiny
Date: Sun Feb 23 2020 - 10:04:59 EST

On Fri, Feb 21, 2020 at 04:31:09PM -0800, Darrick J. Wong wrote:
> On Thu, Feb 20, 2020 at 04:41:30PM -0800, ira.weiny@xxxxxxxxx wrote:
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > XFS requires the use of the aops of an inode to quiesced prior to
> > changing it to/from the DAX aops vector.
> >
> > Take the aops write lock while changing DAX state.
> >
> > We define a new XFS_DAX_EXCL lock type to carry the lock through to
> > transaction completion.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > ---
> > Changes from v3:
> > Change locking function names to reflect changes in previous
> > patches.
> >
> > Changes from V2:
> > Change name of patch (WAS: fs/xfs: Add lock/unlock state to xfs)
> > Remove the xfs specific lock and move to the vfs layer.
> > We still use XFS_LOCK_DAX_EXCL to be able to pass this
> > flag through to the transaction code. But we no longer
> > have a lock specific to xfs. This removes a lot of code
> > from the XFS layer, preps us for using this in ext4, and
> > is actually more straight forward now that all the
> > locking requirements are better known.
> >
> > Fix locking order comment
> > Rework for new 'state' names
> > (Other comments on the previous patch are not applicable with
> > new patch as much of the code was removed in favor of the vfs
> > level lock)
> > ---
> > fs/xfs/xfs_inode.c | 22 ++++++++++++++++++++--
> > fs/xfs/xfs_inode.h | 7 +++++--
> > 2 files changed, 25 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 35df324875db..5b014c428f0f 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -142,12 +142,12 @@ xfs_ilock_attr_map_shared(
> > *
> > * Basic locking order:
> > *
> > - * i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
> > + * s_dax_sem -> i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
>
> "dax_sem"? I thought this was now called i_aops_sem?

:-/ yep...

>
> > *
> > * mmap_sem locking order:
> > *
> > * i_rwsem -> page lock -> mmap_sem
> > - * mmap_sem -> i_mmap_lock -> page_lock
> > + * s_dax_sem -> mmap_sem -> i_mmap_lock -> page_lock
> > *
> > * The difference in mmap_sem locking order mean that we cannot hold the
> > * i_mmap_lock over syscall based read(2)/write(2) based IO. These IO paths can
> > @@ -182,6 +182,9 @@ xfs_ilock(
> > (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
> > ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
> >
> > + if (lock_flags & XFS_DAX_EXCL)
>
> And similarly, I think this should be XFS_OPSLOCK_EXCL...

... and ... yes...

Thanks for the review, I'll clean it up.

Ira

>
> --D
>
> > + inode_aops_down_write(VFS_I(ip));
> > +
> > if (lock_flags & XFS_IOLOCK_EXCL) {
> > down_write_nested(&VFS_I(ip)->i_rwsem,
> > XFS_IOLOCK_DEP(lock_flags));
> > @@ -224,6 +227,8 @@ xfs_ilock_nowait(
> > * You can't set both SHARED and EXCL for the same lock,
> > * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
> > * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
> > + *
> > + * XFS_DAX_* is not allowed
> > */
> > ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
> > (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
> > @@ -232,6 +237,7 @@ xfs_ilock_nowait(
> > ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
> > (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
> > ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
> > + ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
> >
> > if (lock_flags & XFS_IOLOCK_EXCL) {
> > if (!down_write_trylock(&VFS_I(ip)->i_rwsem))
> > @@ -318,6 +324,9 @@ xfs_iunlock(
> > else if (lock_flags & XFS_ILOCK_SHARED)
> > mrunlock_shared(&ip->i_lock);
> >
> > + if (lock_flags & XFS_DAX_EXCL)
> > + inode_aops_up_write(VFS_I(ip));
> > +
> > trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
> > }
> >
> > @@ -333,6 +342,8 @@ xfs_ilock_demote(
> > ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL));
> > ASSERT((lock_flags &
> > ~(XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);
> > + /* XFS_DAX_* is not allowed */
> > + ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
> >
> > if (lock_flags & XFS_ILOCK_EXCL)
> > mrdemote(&ip->i_lock);
> > @@ -465,6 +476,9 @@ xfs_lock_inodes(
> > ASSERT(!(lock_mode & XFS_ILOCK_EXCL) ||
> > inodes <= XFS_ILOCK_MAX_SUBCLASS + 1);
> >
> > + /* XFS_DAX_* is not allowed */
> > + ASSERT((lock_mode & XFS_DAX_EXCL) == 0);
> > +
> > if (lock_mode & XFS_IOLOCK_EXCL) {
> > ASSERT(!(lock_mode & (XFS_MMAPLOCK_EXCL | XFS_ILOCK_EXCL)));
> > } else if (lock_mode & XFS_MMAPLOCK_EXCL)
> > @@ -566,6 +580,10 @@ xfs_lock_two_inodes(
> > ASSERT(!(ip0_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL)) ||
> > !(ip1_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)));
> >
> > + /* XFS_DAX_* is not allowed */
> > + ASSERT((ip0_mode & XFS_DAX_EXCL) == 0);
> > + ASSERT((ip1_mode & XFS_DAX_EXCL) == 0);
> > +
> > ASSERT(ip0->i_ino != ip1->i_ino);
> >
> > if (ip0->i_ino > ip1->i_ino) {
> > diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> > index 492e53992fa9..25fe20740bf7 100644
> > --- a/fs/xfs/xfs_inode.h
> > +++ b/fs/xfs/xfs_inode.h
> > @@ -278,10 +278,12 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
> > #define XFS_ILOCK_SHARED (1<<3)
> > #define XFS_MMAPLOCK_EXCL (1<<4)
> > #define XFS_MMAPLOCK_SHARED (1<<5)
> > +#define XFS_DAX_EXCL (1<<6)
> >
> > #define XFS_LOCK_MASK (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
> > | XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
> > - | XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)
> > + | XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED \
> > + | XFS_DAX_EXCL)
> >
> > #define XFS_LOCK_FLAGS \
> > { XFS_IOLOCK_EXCL, "IOLOCK_EXCL" }, \
> > @@ -289,7 +291,8 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
> > { XFS_ILOCK_EXCL, "ILOCK_EXCL" }, \
> > { XFS_ILOCK_SHARED, "ILOCK_SHARED" }, \
> > { XFS_MMAPLOCK_EXCL, "MMAPLOCK_EXCL" }, \
> > - { XFS_MMAPLOCK_SHARED, "MMAPLOCK_SHARED" }
> > + { XFS_MMAPLOCK_SHARED, "MMAPLOCK_SHARED" }, \
> > + { XFS_DAX_EXCL, "DAX_EXCL" }
> >
> >
> > /*
> > --
> > 2.21.0
> >