On Wed, Sep 23, 2020 at 03:48:59AM +0100, Matthew Wilcox wrote: > On Tue, Sep 22, 2020 at 09:06:03PM -0400, Qian Cai wrote: > > On Tue, 2020-09-22 at 18:05 +0100, Matthew Wilcox wrote: > > > On Tue, Sep 22, 2020 at 12:23:45PM -0400, Qian Cai wrote: > > > > On Fri, 2020-09-11 at 00:47 +0100, Matthew Wilcox (Oracle) wrote: > > > > > Size the uptodate array dynamically to support larger pages in the > > > > > page cache. With a 64kB page, we're only saving 8 bytes per page today, > > > > > but with a 2MB maximum page size, we'd have to allocate more than 4kB > > > > > per page. Add a few debugging assertions. > > > > > > > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > > > > > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> > > > > > > > > Some syscall fuzzing will trigger this on powerpc: > > > > > > > > .config: https://gitlab.com/cailca/linux-mm/-/blob/master/powerpc.config > > > > > > > > [ 8805.895344][T445431] WARNING: CPU: 61 PID: 445431 at fs/iomap/buffered- > > > > io.c:78 iomap_page_release+0x250/0x270 > > > > > > Well, I'm glad it triggered. That warning is: > > > WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) != > > > PageUptodate(page)); > > > so there was definitely a problem of some kind. > > > > > > truncate_cleanup_page() calls > > > do_invalidatepage() calls > > > iomap_invalidatepage() calls > > > iomap_page_release() > > > > > > Is this the first warning? I'm wondering if maybe there was an I/O error > > > earlier which caused PageUptodate to get cleared again. If it's easy to > > > reproduce, perhaps you could try something like this? > > > > > > +void dump_iomap_page(struct page *page, const char *reason) > > > +{ > > > + struct iomap_page *iop = to_iomap_page(page); > > > + unsigned int nr_blocks = i_blocks_per_page(page->mapping->host, page); > > > + > > > + dump_page(page, reason); > > > + if (iop) > > > + printk("iop:reads %d writes %d uptodate %*pb\n", > > > + atomic_read(&iop->read_bytes_pending), > > > + atomic_read(&iop->write_bytes_pending), > > > + nr_blocks, iop->uptodate); > > > + else > > > + printk("iop:none\n"); > > > +} > > > > > > and then do something like: > > > > > > if (bitmap_full(iop->uptodate, nr_blocks) != PageUptodate(page)) > > > dump_iomap_page(page, NULL); > > > > This: > > > > [ 1683.158254][T164965] page:000000004a6c16cd refcount:2 mapcount:0 mapping:00000000ea017dc5 index:0x2 pfn:0xc365c > > [ 1683.158311][T164965] aops:xfs_address_space_operations ino:417b7e7 dentry name:"trinity-testfile2" > > [ 1683.158354][T164965] flags: 0x7fff8000000015(locked|uptodate|lru) > > [ 1683.158392][T164965] raw: 007fff8000000015 c00c0000019c4b08 c00c0000019a53c8 c000201c8362c1e8 > > [ 1683.158430][T164965] raw: 0000000000000002 0000000000000000 00000002ffffffff c000201c54db4000 > > [ 1683.158470][T164965] page->mem_cgroup:c000201c54db4000 > > [ 1683.158506][T164965] iop:none > > Oh, I'm a fool. This is after the call to detach_page_private() so > page->private is NULL and we don't get the iop dumped. > > Nevertheless, this is interesting. Somehow, the page is marked Uptodate, > but the bitmap is deemed not full. There are three places where we set > an iomap page Uptodate: > > 1. if (bitmap_full(iop->uptodate, i_blocks_per_page(inode, page))) > SetPageUptodate(page); > > 2. if (page_has_private(page)) > iomap_iop_set_range_uptodate(page, off, len); > else > SetPageUptodate(page); > > 3. BUG_ON(page->index); > ... > SetPageUptodate(page); > > It can't be #2 because the page has an iop. It can't be #3 because the > page->index is not 0. So at some point in the past, the bitmap was full. > > I don't think it's possible for inode->i_blksize to change, and you > aren't running with THPs, so it's definitely not possible for thp_size() > to change. So i_blocks_per_page() isn't going to change. > > We seem to have allocated enough memory for ->iop because that's also > based on i_blocks_per_page(). > > I'm out of ideas. Maybe I'll wake up with a better idea in the morning. > I've been trying to reproduce this on x86 with a 1kB block size > filesystem, and haven't been able to yet. Maybe I'll try to setup a > powerpc cross-compilation environment tomorrow. FWIW I managed to reproduce it with the following fstests configuration on a 1k block size fs on a x86 machinE: SECTION -- -no-sections- FSTYP -- xfs MKFS_OPTIONS -- -m reflink=1,rmapbt=1 -i sparse=1 -b size=1024 MOUNT_OPTIONS -- -o usrquota,grpquota,prjquota HOST_OPTIONS -- local.config CHECK_OPTIONS -- -g auto XFS_MKFS_OPTIONS -- -bsize=4096 TIME_FACTOR -- 1 LOAD_FACTOR -- 1 TEST_DIR -- /mnt TEST_DEV -- /dev/sde SCRATCH_DEV -- /dev/sdd SCRATCH_MNT -- /opt OVL_UPPER -- ovl-upper OVL_LOWER -- ovl-lower OVL_WORK -- ovl-work KERNEL -- 5.9.0-rc4-djw The kernel is more or less iomap-for-next. --D
