| Message ID | 20230202204428.3267832-5-willy@infradead.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Fix a minor POSIX conformance problem | expand |
Matthew Wilcox (Oracle) <willy@infradead.org> wrote: > POSIX requires that "If the file size is increased, the extended area > shall appear as if it were zero-filled". It is possible to use mmap to > write past EOF and that data will become visible instead of zeroes. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> That seems to work. Do you want me to pass it on to Linus? If not: Acked-by: David Howells <dhowells@redhat.com>
On Mon, Feb 27, 2023 at 01:49:27PM +0000, David Howells wrote: > Matthew Wilcox (Oracle) <willy@infradead.org> wrote: > > > POSIX requires that "If the file size is increased, the extended area > > shall appear as if it were zero-filled". It is possible to use mmap to > > write past EOF and that data will become visible instead of zeroes. > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > That seems to work. Do you want me to pass it on to Linus? If not: > > Acked-by: David Howells <dhowells@redhat.com> I'll send a patch series with all of this; it doesn't seem terribly urgent. Do you think there's a similar problem for AFS that Brian noted with the generic patch?
Matthew Wilcox <willy@infradead.org> wrote: > I'll send a patch series with all of this; it doesn't seem terribly > urgent. Do you think there's a similar problem for AFS that Brian > noted with the generic patch? Do you have a link I can look at? David
Matthew Wilcox <willy@infradead.org> wrote: > I'll send a patch series with all of this; it doesn't seem terribly > urgent. Do you think there's a similar problem for AFS that Brian > noted with the generic patch? Probably not. To avoid deadlocking itself, afs uses a mutex to prevent writepages racing with truncate (vnode->validate_lock). commit ec0fa0b659144d9c68204d23f627b6a65fa53e50 afs: Fix deadlock between writeback and truncate the afs_setattr_edit_file() call that changes i_size and partially clears the pagecache is applied to the local inode before the mutex is dropped. David
diff --git a/fs/afs/inode.c b/fs/afs/inode.c index 6d3a3dbe4928..92e2ba7625de 100644 --- a/fs/afs/inode.c +++ b/fs/afs/inode.c @@ -854,6 +854,8 @@ static void afs_setattr_edit_file(struct afs_operation *op) if (size < i_size) truncate_pagecache(inode, size); + else + truncate_pagecache(inode, i_size); if (size != i_size) fscache_resize_cookie(afs_vnode_cache(vp->vnode), vp->scb.status.size);
POSIX requires that "If the file size is increased, the extended area shall appear as if it were zero-filled". It is possible to use mmap to write past EOF and that data will become visible instead of zeroes. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- fs/afs/inode.c | 2 ++ 1 file changed, 2 insertions(+)