Re: [PATCH 07/13] xfs: Convert to use invalidate_lock

Darrick J. Wong
2021-05-25T21:37:33Z

On Tue, May 25, 2021 at 03:50:44PM +0200, Jan Kara wrote:
> Use invalidate_lock instead of XFS internal i_mmap_lock. The intended
> purpose of invalidate_lock is exactly the same. Note that the locking in
> __xfs_filemap_fault() slightly changes as filemap_fault() already takes
> invalidate_lock.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> CC: <linux-xfs@vger.kernel.org>
> CC: "Darrick J. Wong" <darrick.wong@oracle.com>

It's djwong@kernel.org now.

> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/xfs/xfs_file.c | 12 ++++++-----
> fs/xfs/xfs_inode.c | 52 ++++++++++++++++++++++++++--------------------
> fs/xfs/xfs_inode.h | 1 -
> fs/xfs/xfs_super.c | 2 --
> 4 files changed, 36 insertions(+), 31 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 396ef36dcd0a..dc9cb5c20549 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1282,7 +1282,7 @@ xfs_file_llseek(
> *
> * mmap_lock (MM)
> * sb_start_pagefault(vfs, freeze)
> - * i_mmaplock (XFS - truncate serialisation)
> + * invalidate_lock (vfs/XFS_MMAPLOCK - truncate serialisation)
> * page_lock (MM)
> * i_lock (XFS - extent map serialisation)
> */
> @@ -1303,24 +1303,26 @@ __xfs_filemap_fault(
> file_update_time(vmf->vma->vm_file);
> }
>
> - xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> if (IS_DAX(inode)) {
> pfn_t pfn;
>
> + xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL,
> (write_fault && !vmf->cow_page) ?
> &xfs_direct_write_iomap_ops :
> &xfs_read_iomap_ops);
> if (ret & VM_FAULT_NEEDDSYNC)
> ret = dax_finish_sync_fault(vmf, pe_size, pfn);
> + xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> } else {
> - if (write_fault)
> + if (write_fault) {
> + xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> ret = iomap_page_mkwrite(vmf,
> &xfs_buffered_write_iomap_ops);
> - else
> + xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> + } else
> ret = filemap_fault(vmf);
> }
> - xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
>
> if (write_fault)
> sb_end_pagefault(inode->i_sb);
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 0369eb22c1bb..53bb5fc33621 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -131,7 +131,7 @@ xfs_ilock_attr_map_shared(
>
> /*
> * In addition to i_rwsem in the VFS inode, the xfs inode contains 2
> - * multi-reader locks: i_mmap_lock and the i_lock. This routine allows
> + * multi-reader locks: invalidate_lock and the i_lock. This routine allows
> * various combinations of the locks to be obtained.
> *
> * The 3 locks should always be ordered so that the IO lock is obtained first,
> @@ -139,23 +139,23 @@ xfs_ilock_attr_map_shared(
> *
> * Basic locking order:
> *
> - * i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
> + * i_rwsem -> invalidate_lock -> page_lock -> i_ilock
> *
> * mmap_lock locking order:
> *
> * i_rwsem -> page lock -> mmap_lock
> - * mmap_lock -> i_mmap_lock -> page_lock
> + * mmap_lock -> invalidate_lock -> page_lock
> *
> * The difference in mmap_lock locking order mean that we cannot hold the
> - * i_mmap_lock over syscall based read(2)/write(2) based IO. These IO paths can
> - * fault in pages during copy in/out (for buffered IO) or require the mmap_lock
> - * in get_user_pages() to map the user pages into the kernel address space for
> - * direct IO. Similarly the i_rwsem cannot be taken inside a page fault because
> - * page faults already hold the mmap_lock.
> + * invalidate_lock over syscall based read(2)/write(2) based IO. These IO paths
> + * can fault in pages during copy in/out (for buffered IO) or require the
> + * mmap_lock in get_user_pages() to map the user pages into the kernel address
> + * space for direct IO. Similarly the i_rwsem cannot be taken inside a page
> + * fault because page faults already hold the mmap_lock.
> *
> * Hence to serialise fully against both syscall and mmap based IO, we need to
> - * take both the i_rwsem and the i_mmap_lock. These locks should *only* be both
> - * taken in places where we need to invalidate the page cache in a race
> + * take both the i_rwsem and the invalidate_lock. These locks should *only* be
> + * both taken in places where we need to invalidate the page cache in a race
> * free manner (e.g. truncate, hole punch and other extent manipulation
> * functions).
> */
> @@ -187,10 +187,13 @@ xfs_ilock(
> XFS_IOLOCK_DEP(lock_flags));
> }
>
> - if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrupdate_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
> - else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mraccess_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
> + if (lock_flags & XFS_MMAPLOCK_EXCL) {
> + down_write_nested(&VFS_I(ip)->i_mapping->invalidate_lock,
> + XFS_MMAPLOCK_DEP(lock_flags));
> + } else if (lock_flags & XFS_MMAPLOCK_SHARED) {
> + down_read_nested(&VFS_I(ip)->i_mapping->invalidate_lock,
> + XFS_MMAPLOCK_DEP(lock_flags));
> + }
>
> if (lock_flags & XFS_ILOCK_EXCL)
> mrupdate_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
> @@ -239,10 +242,10 @@ xfs_ilock_nowait(
> }
>
> if (lock_flags & XFS_MMAPLOCK_EXCL) {
> - if (!mrtryupdate(&ip->i_mmaplock))
> + if (!down_write_trylock(&VFS_I(ip)->i_mapping->invalidate_lock))
> goto out_undo_iolock;
> } else if (lock_flags & XFS_MMAPLOCK_SHARED) {
> - if (!mrtryaccess(&ip->i_mmaplock))
> + if (!down_read_trylock(&VFS_I(ip)->i_mapping->invalidate_lock))
> goto out_undo_iolock;
> }
>
> @@ -257,9 +260,9 @@ xfs_ilock_nowait(
>
> out_undo_mmaplock:
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrunlock_excl(&ip->i_mmaplock);
> + up_write(&VFS_I(ip)->i_mapping->invalidate_lock);
> else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mrunlock_shared(&ip->i_mmaplock);
> + up_read(&VFS_I(ip)->i_mapping->invalidate_lock);
> out_undo_iolock:
> if (lock_flags & XFS_IOLOCK_EXCL)
> up_write(&VFS_I(ip)->i_rwsem);
> @@ -306,9 +309,9 @@ xfs_iunlock(
> up_read(&VFS_I(ip)->i_rwsem);
>
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrunlock_excl(&ip->i_mmaplock);
> + up_write(&VFS_I(ip)->i_mapping->invalidate_lock);
> else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mrunlock_shared(&ip->i_mmaplock);
> + up_read(&VFS_I(ip)->i_mapping->invalidate_lock);
>
> if (lock_flags & XFS_ILOCK_EXCL)
> mrunlock_excl(&ip->i_lock);
> @@ -334,7 +337,7 @@ xfs_ilock_demote(
> if (lock_flags & XFS_ILOCK_EXCL)
> mrdemote(&ip->i_lock);
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrdemote(&ip->i_mmaplock);
> + downgrade_write(&VFS_I(ip)->i_mapping->invalidate_lock);
> if (lock_flags & XFS_IOLOCK_EXCL)
> downgrade_write(&VFS_I(ip)->i_rwsem);
>
> @@ -355,8 +358,11 @@ xfs_isilocked(
>
> if (lock_flags & (XFS_MMAPLOCK_EXCL|XFS_MMAPLOCK_SHARED)) {
> if (!(lock_flags & XFS_MMAPLOCK_SHARED))
> - return !!ip->i_mmaplock.mr_writer;
> - return rwsem_is_locked(&ip->i_mmaplock.mr_lock);
> + return !debug_locks ||
> + lockdep_is_held_type(
> + &VFS_I(ip)->i_mapping->invalidate_lock,
> + 0);
> + return rwsem_is_locked(&VFS_I(ip)->i_mapping->invalidate_lock);

This doesn't look right...

If lockdep is disabled, we always return true for
xfs_isilocked(ip, XFS_MMAPLOCK_EXCL) even if nobody holds the lock?

Granted, you probably just copy-pasted from the IOLOCK_SHARED clause
beneath it. Er... oh right, preichl was messing with all that...

https://lore.kernel.org/linux-xfs/20201016021005.548850-2-preichl@redhat.com/

I guess I'll go have a look at that again.

--D

> }
>
> if (lock_flags & (XFS_IOLOCK_EXCL|XFS_IOLOCK_SHARED)) {
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index ca826cfba91c..a0e4153efbbe 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -40,7 +40,6 @@ typedef struct xfs_inode {
> /* Transaction and locking information. */
> struct xfs_inode_log_item *i_itemp; /* logging information */
> mrlock_t i_lock; /* inode lock */
> - mrlock_t i_mmaplock; /* inode mmap IO lock */
> atomic_t i_pincount; /* inode pin count */
>
> /*
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index a2dab05332ac..eeaf44910b5f 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -715,8 +715,6 @@ xfs_fs_inode_init_once(
> atomic_set(&ip->i_pincount, 0);
> spin_lock_init(&ip->i_flags_lock);
>
> - mrlock_init(&ip->i_mmaplock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> - "xfsino", ip->i_ino);
> mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> "xfsino", ip->i_ino);
> }
> --
> 2.26.2
>