On Tue 19-12-17 17:11:38, Dan Williams wrote:
> On Fri, Nov 10, 2017 at 1:08 AM, Christoph Hellwig <hch@xxxxxx> wrote:
> >> + struct {
> >> + /*
> >> + * ZONE_DEVICE pages are never on an lru or handled by
> >> + * a slab allocator, this points to the hosting device
> >> + * page map.
> >> + */
> >> + struct dev_pagemap *pgmap;
> >> + /*
> >> + * inode association for MEMORY_DEVICE_FS_DAX page-idle
> >> + * callbacks. Note that we don't use ->mapping since
> >> + * that has hard coded page-cache assumptions in
> >> + * several paths.
> >> + */
> >
> > What assumptions? I'd much rather fix those up than having two fields
> > that have the same functionality.
>
> [ Reviving this old thread where you asked why I introduce page->inode
> instead of reusing page->mapping ]
>
> For example, xfs_vm_set_page_dirty() assumes that page->mapping being
> non-NULL indicates a typical page cache page, this is a false
> assumption for DAX. My guess at a fix for this is to add
> pagecache_page() checks to locations like this, but I worry about how
> to find them all. Where pagecache_page() is:
>
> bool pagecache_page(struct page *page)
> {
> if (!page->mapping)
> return false;
> if (!IS_DAX(page->mapping->host))
> return false;
> return true;
> }
>
> Otherwise we go off the rails:
>
> WARNING: CPU: 27 PID: 1783 at fs/xfs/xfs_aops.c:1468
> xfs_vm_set_page_dirty+0xf3/0x1b0 [xfs]
But this just shows that mapping->a_ops are wrong for this mapping, doesn't
it? ->set_page_dirty handler for DAX mapping should just properly handle
DAX pages... (and only those)
> [..]
> CPU: 27 PID: 1783 Comm: dma-collision Tainted: G O
> 4.15.0-rc2+ #984
> [..]
> Call Trace:
> set_page_dirty_lock+0x40/0x60
> bio_set_pages_dirty+0x37/0x50
> iomap_dio_actor+0x2b7/0x3b0
> ? iomap_dio_zero+0x110/0x110
> iomap_apply+0xa4/0x110
> iomap_dio_rw+0x29e/0x3b0
> ? iomap_dio_zero+0x110/0x110
> ? xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
> xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
> xfs_file_read_iter+0xa0/0xc0 [xfs]
> __vfs_read+0xf9/0x170
> vfs_read+0xa6/0x150
> SyS_pread64+0x93/0xb0
> entry_SYSCALL_64_fastpath+0x1f/0x96
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
