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Message-ID: <20250113024940.GW1306365@frogsfrogsfrogs>
Date: Sun, 12 Jan 2025 18:49:40 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Alistair Popple <apopple@...dia.com>
Cc: akpm@...ux-foundation.org, dan.j.williams@...el.com, linux-mm@...ck.org,
alison.schofield@...el.com, lina@...hilina.net,
zhang.lyra@...il.com, gerald.schaefer@...ux.ibm.com,
vishal.l.verma@...el.com, dave.jiang@...el.com, logang@...tatee.com,
bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca,
catalin.marinas@....com, will@...nel.org, mpe@...erman.id.au,
npiggin@...il.com, dave.hansen@...ux.intel.com, ira.weiny@...el.com,
willy@...radead.org, tytso@....edu, linmiaohe@...wei.com,
david@...hat.com, peterx@...hat.com, linux-doc@...r.kernel.org,
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linuxppc-dev@...ts.ozlabs.org, nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
jhubbard@...dia.com, hch@....de, david@...morbit.com,
chenhuacai@...nel.org, kernel@...0n.name, loongarch@...ts.linux.dev
Subject: Re: [PATCH v6 07/26] fs/dax: Ensure all pages are idle prior to
filesystem unmount
On Mon, Jan 13, 2025 at 11:57:18AM +1100, Alistair Popple wrote:
> On Fri, Jan 10, 2025 at 08:50:19AM -0800, Darrick J. Wong wrote:
> > On Fri, Jan 10, 2025 at 05:00:35PM +1100, Alistair Popple wrote:
> > > File systems call dax_break_mapping() prior to reallocating file
> > > system blocks to ensure the page is not undergoing any DMA or other
> > > accesses. Generally this is needed when a file is truncated to ensure
> > > that if a block is reallocated nothing is writing to it. However
> > > filesystems currently don't call this when an FS DAX inode is evicted.
> > >
> > > This can cause problems when the file system is unmounted as a page
> > > can continue to be under going DMA or other remote access after
> > > unmount. This means if the file system is remounted any truncate or
> > > other operation which requires the underlying file system block to be
> > > freed will not wait for the remote access to complete. Therefore a
> > > busy block may be reallocated to a new file leading to corruption.
> > >
> > > Signed-off-by: Alistair Popple <apopple@...dia.com>
> > >
> > > ---
> > >
> > > Changes for v5:
> > >
> > > - Don't wait for pages to be idle in non-DAX mappings
> > > ---
> > > fs/dax.c | 29 +++++++++++++++++++++++++++++
> > > fs/ext4/inode.c | 32 ++++++++++++++------------------
> > > fs/xfs/xfs_inode.c | 9 +++++++++
> > > fs/xfs/xfs_inode.h | 1 +
> > > fs/xfs/xfs_super.c | 18 ++++++++++++++++++
> > > include/linux/dax.h | 2 ++
> > > 6 files changed, 73 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/fs/dax.c b/fs/dax.c
> > > index 7008a73..4e49cc4 100644
> > > --- a/fs/dax.c
> > > +++ b/fs/dax.c
> > > @@ -883,6 +883,14 @@ static int wait_page_idle(struct page *page,
> > > TASK_INTERRUPTIBLE, 0, 0, cb(inode));
> > > }
> > >
> > > +static void wait_page_idle_uninterruptible(struct page *page,
> > > + void (cb)(struct inode *),
> > > + struct inode *inode)
> > > +{
> > > + ___wait_var_event(page, page_ref_count(page) == 1,
> > > + TASK_UNINTERRUPTIBLE, 0, 0, cb(inode));
> > > +}
> > > +
> > > /*
> > > * Unmaps the inode and waits for any DMA to complete prior to deleting the
> > > * DAX mapping entries for the range.
> > > @@ -911,6 +919,27 @@ int dax_break_mapping(struct inode *inode, loff_t start, loff_t end,
> > > }
> > > EXPORT_SYMBOL_GPL(dax_break_mapping);
> > >
> > > +void dax_break_mapping_uninterruptible(struct inode *inode,
> > > + void (cb)(struct inode *))
> > > +{
> > > + struct page *page;
> > > +
> > > + if (!dax_mapping(inode->i_mapping))
> > > + return;
> > > +
> > > + do {
> > > + page = dax_layout_busy_page_range(inode->i_mapping, 0,
> > > + LLONG_MAX);
> > > + if (!page)
> > > + break;
> > > +
> > > + wait_page_idle_uninterruptible(page, cb, inode);
> > > + } while (true);
> > > +
> > > + dax_delete_mapping_range(inode->i_mapping, 0, LLONG_MAX);
> > > +}
> > > +EXPORT_SYMBOL_GPL(dax_break_mapping_uninterruptible);
> > > +
> > > /*
> > > * Invalidate DAX entry if it is clean.
> > > */
> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > > index ee8e83f..fa35161 100644
> > > --- a/fs/ext4/inode.c
> > > +++ b/fs/ext4/inode.c
> > > @@ -163,6 +163,18 @@ int ext4_inode_is_fast_symlink(struct inode *inode)
> > > (inode->i_size < EXT4_N_BLOCKS * 4);
> > > }
> > >
> > > +static void ext4_wait_dax_page(struct inode *inode)
> > > +{
> > > + filemap_invalidate_unlock(inode->i_mapping);
> > > + schedule();
> > > + filemap_invalidate_lock(inode->i_mapping);
> > > +}
> > > +
> > > +int ext4_break_layouts(struct inode *inode)
> > > +{
> > > + return dax_break_mapping_inode(inode, ext4_wait_dax_page);
> > > +}
> > > +
> > > /*
> > > * Called at the last iput() if i_nlink is zero.
> > > */
> > > @@ -181,6 +193,8 @@ void ext4_evict_inode(struct inode *inode)
> > >
> > > trace_ext4_evict_inode(inode);
> > >
> > > + dax_break_mapping_uninterruptible(inode, ext4_wait_dax_page);
> > > +
> > > if (EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)
> > > ext4_evict_ea_inode(inode);
> > > if (inode->i_nlink) {
> > > @@ -3902,24 +3916,6 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
> > > return ret;
> > > }
> > >
> > > -static void ext4_wait_dax_page(struct inode *inode)
> > > -{
> > > - filemap_invalidate_unlock(inode->i_mapping);
> > > - schedule();
> > > - filemap_invalidate_lock(inode->i_mapping);
> > > -}
> > > -
> > > -int ext4_break_layouts(struct inode *inode)
> > > -{
> > > - struct page *page;
> > > - int error;
> > > -
> > > - if (WARN_ON_ONCE(!rwsem_is_locked(&inode->i_mapping->invalidate_lock)))
> > > - return -EINVAL;
> > > -
> > > - return dax_break_mapping_inode(inode, ext4_wait_dax_page);
> > > -}
> > > -
> > > /*
> > > * ext4_punch_hole: punches a hole in a file by releasing the blocks
> > > * associated with the given offset and length
> > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > > index 4410b42..c7ec5ab 100644
> > > --- a/fs/xfs/xfs_inode.c
> > > +++ b/fs/xfs/xfs_inode.c
> > > @@ -2997,6 +2997,15 @@ xfs_break_dax_layouts(
> > > return dax_break_mapping_inode(inode, xfs_wait_dax_page);
> > > }
> > >
> > > +void
> > > +xfs_break_dax_layouts_uninterruptible(
> > > + struct inode *inode)
> > > +{
> > > + xfs_assert_ilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL);
> > > +
> > > + dax_break_mapping_uninterruptible(inode, xfs_wait_dax_page);
> > > +}
> > > +
> > > int
> > > xfs_break_layouts(
> > > struct inode *inode,
> > > diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> > > index c4f03f6..613797a 100644
> > > --- a/fs/xfs/xfs_inode.h
> > > +++ b/fs/xfs/xfs_inode.h
> > > @@ -594,6 +594,7 @@ xfs_itruncate_extents(
> > > }
> > >
> > > int xfs_break_dax_layouts(struct inode *inode);
> > > +void xfs_break_dax_layouts_uninterruptible(struct inode *inode);
> > > int xfs_break_layouts(struct inode *inode, uint *iolock,
> > > enum layout_break_reason reason);
> > >
> > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > > index 8524b9d..73ec060 100644
> > > --- a/fs/xfs/xfs_super.c
> > > +++ b/fs/xfs/xfs_super.c
> > > @@ -751,6 +751,23 @@ xfs_fs_drop_inode(
> > > return generic_drop_inode(inode);
> > > }
> > >
> > > +STATIC void
> > > +xfs_fs_evict_inode(
> > > + struct inode *inode)
> > > +{
> > > + struct xfs_inode *ip = XFS_I(inode);
> > > + uint iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
> > > +
> > > + if (IS_DAX(inode)) {
> > > + xfs_ilock(ip, iolock);
> > > + xfs_break_dax_layouts_uninterruptible(inode);
> > > + xfs_iunlock(ip, iolock);
> >
> > If we're evicting the inode, why is it necessary to take i_rwsem and the
> > mmap invalidation lock? Shouldn't the evicting thread be the only one
> > with access to this inode?
>
> Hmm, good point. I think you're right. I can easily stop taking
> XFS_IOLOCK_EXCL. Not taking XFS_MMAPLOCK_EXCL is slightly more difficult because
> xfs_wait_dax_page() expects it to be taken. Do you think it is worth creating a
> separate callback (xfs_wait_dax_page_unlocked()?) specifically for this path or
> would you be happy with a comment explaining why we take the XFS_MMAPLOCK_EXCL
> lock here?
There shouldn't be any other threads removing "pages" from i_mapping
during eviction, right? If so, I think you can just call schedule()
directly from dax_break_mapping_uninterruptble.
(dax mappings aren't allowed supposed to persist beyond unmount /
eviction, just like regular pagecache, right??)
--D
> - Alistair
>
> > --D
> >
> > > + }
> > > +
> > > + truncate_inode_pages_final(&inode->i_data);
> > > + clear_inode(inode);
> > > +}
> > > +
> > > static void
> > > xfs_mount_free(
> > > struct xfs_mount *mp)
> > > @@ -1189,6 +1206,7 @@ static const struct super_operations xfs_super_operations = {
> > > .destroy_inode = xfs_fs_destroy_inode,
> > > .dirty_inode = xfs_fs_dirty_inode,
> > > .drop_inode = xfs_fs_drop_inode,
> > > + .evict_inode = xfs_fs_evict_inode,
> > > .put_super = xfs_fs_put_super,
> > > .sync_fs = xfs_fs_sync_fs,
> > > .freeze_fs = xfs_fs_freeze,
> > > diff --git a/include/linux/dax.h b/include/linux/dax.h
> > > index ef9e02c..7c3773f 100644
> > > --- a/include/linux/dax.h
> > > +++ b/include/linux/dax.h
> > > @@ -274,6 +274,8 @@ static inline int __must_check dax_break_mapping_inode(struct inode *inode,
> > > {
> > > return dax_break_mapping(inode, 0, LLONG_MAX, cb);
> > > }
> > > +void dax_break_mapping_uninterruptible(struct inode *inode,
> > > + void (cb)(struct inode *));
> > > int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> > > struct inode *dest, loff_t destoff,
> > > loff_t len, bool *is_same,
> > > --
> > > git-series 0.9.1
> > >
>
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