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Date: Mon, 13 Jan 2020 17:30:04 -0800 From: "Darrick J. Wong" <darrick.wong@...cle.com> To: Ira Weiny <ira.weiny@...el.com> Cc: linux-kernel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>, Dan Williams <dan.j.williams@...el.com>, Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>, "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed On Mon, Jan 13, 2020 at 04:46:10PM -0800, Ira Weiny wrote: > On Mon, Jan 13, 2020 at 02:22:12PM -0800, Darrick J. Wong wrote: > > On Fri, Jan 10, 2020 at 11:29:39AM -0800, ira.weiny@...el.com wrote: > > > From: Ira Weiny <ira.weiny@...el.com> > > > > > [snip] > > > > > > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c > > > index bc3654fe3b5d..1ab0906c6c7f 100644 > > > --- a/fs/xfs/xfs_ioctl.c > > > +++ b/fs/xfs/xfs_ioctl.c > > > @@ -1200,6 +1200,14 @@ xfs_ioctl_setattr_dax_invalidate( > > > goto out_unlock; > > > } > > > > > > + /* > > > + * If there is a mapping in place we must remain in our current mode. > > > + */ > > > + if (atomic64_read(&inode->i_mapped)) { > > > > Urk, should we really be messing around with the address space > > internals? > > I contemplated a function call instead of checking i_mapped directly? Is that > what you mean? Yeah. Abstracting the details just enough that filesystems don't have to know that i_mapped is atomic64 etc. > > > > > > + error = -EBUSY; > > > + goto out_unlock; > > > + } > > > + > > > error = filemap_write_and_wait(inode->i_mapping); > > > if (error) > > > goto out_unlock; > > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > > index 631f11d6246e..6e7dc626b657 100644 > > > --- a/include/linux/fs.h > > > +++ b/include/linux/fs.h > > > @@ -740,6 +740,7 @@ struct inode { > > > #endif > > > > > > void *i_private; /* fs or device private pointer */ > > > + atomic64_t i_mapped; > > > > I would have expected to find this in struct address_space since the > > mapping count is a function of the address space, right? > > I suppose but the only external call (above) would be passing an inode. So to > me it seemed better here. But the number of memory mappings reflects the state of the address space, not the inode. Or maybe put another way, if I were an mm developer I would not expect to look in struct inode for mm state. static inline bool inode_has_mappings(struct inode *inode) { return atomic64_read(&inode->i_mapping->mapcount) > 0; } OTOH if there exist other mm developers who /do/ find that storing the mmap count in struct inode is more logical, please let me know. :) --D > Ira > > > > > --D > >
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