On Tue, Sep 22, 2020 at 06:05:26PM +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(a)infradead.org>
> > Reviewed-by: Dave Chinner <dchinner(a)redhat.com>
> 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
Well, I'm glad it triggered. That warning is:
WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
so there was definitely a problem of some kind.
OK, I'm pretty sure the problem predated this commit, and it's simply
that I added a warning (looking for something else) that caught this.
I have a tree completly gunked up with debugging code now to try to
understand the problem better, but my guess is that if you put this
warning into a previous version, you'd see the same problem occurring
(and it is a real problem, because we skip writeback of parts of the
page which are !uptodate).