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    SubjectRe: [PATCH V4 09/13] fs/xfs: Add write aops lock to xfs layer
    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@intel.com wrote:
    > > From: Ira Weiny <ira.weiny@intel.com>
    > >
    > > 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@intel.com>
    > >
    > > ---
    > > 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
    > >

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