From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@infradead.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC] what to do with IOCB_DSYNC?
Date: Sun, 22 May 2022 18:25:55 +0000 [thread overview]
Message-ID: <YoqAM1RnN/er6GDP@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <7abc2e36-f2f3-e89c-f549-9edd6633b4a1@kernel.dk>
On Sun, May 22, 2022 at 12:06:24PM -0600, Jens Axboe wrote:
> union {
> + size_t uaddr_len;
WTF for?
> +#define iterate_uaddr(i, n, base, len, off, STEP) { \
> + size_t off = 0; \
> + size_t skip = i->iov_offset; \
> + len = min(n, i->uaddr_len - skip); \
How would you ever get offset past the size? Note that we do
keep track of amount of space left...
> - if (iter_is_iovec(i))
> + if (!i->nofault)
> might_fault();
Nope. Sorry, but by default nofault will be false for *all* types.
It's not "I won't fault", it's "pass FOLL_NOFAULT to g_u_p".
> - if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
> + if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) ||
> + iter_is_uaddr(i) || iov_iter_is_xarray(i)) {
> void *kaddr = kmap_local_page(page);
> size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
> kunmap_local(kaddr);
Nope. This is bogus - _copy_to_iter() *can* legitimately fault for those, so
the same considerations as for iovec apply.
> @@ -900,7 +934,8 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
> return 0;
> if (likely(iter_is_iovec(i)))
> return copy_page_from_iter_iovec(page, offset, bytes, i);
> - if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
> + if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) ||
> + iter_is_uaddr(i) || iov_iter_is_xarray(i)) {
Ditto.
> @@ -1319,6 +1368,14 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
> if (iov_iter_is_bvec(i))
> return iov_iter_alignment_bvec(i);
>
> + if (iter_is_uaddr(i)) {
> + size_t len = i->count - i->iov_offset;
> +
> + if (len)
> + return (unsigned long) i->uaddr + i->iov_offset;
Huh? iov_iter_alignment() wants the worse of beginning and end, if there's
any data at all.
> @@ -1527,6 +1584,9 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
> if (!maxsize)
> return 0;
>
> + if (WARN_ON_ONCE(iter_is_uaddr(i)))
> + return 0;
So no DIO read(2) or write(2) anymore? Harsh...
> @@ -1652,6 +1712,8 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
> maxsize = i->count;
> if (!maxsize)
> return 0;
> + if (WARN_ON_ONCE(iter_is_uaddr(i)))
> + return 0;
Ditto.
> + if (iter_is_uaddr(i)) {
> + unsigned long uaddr = (unsigned long) i->uaddr;
> + unsigned long start, end;
> +
> + end = (uaddr + i->count - i->iov_offset + PAGE_SIZE - 1)
> + >> PAGE_SHIFT;
> + start = uaddr >> PAGE_SHIFT;
> + return min_t(int, end - start, maxpages);
Nope. The value is wrong (sanity check - decrement the base and increment
iov_offset by the same amount; the range of addresses is the same,
and the same should go for the result; yours fails that test).
FWIW, here it's
if (likely(iter_is_ubuf(i))) {
unsigned offs = offset_in_page(i->ubuf + i->iov_offset);
int npages = DIV_ROUND_UP(offs + i->count, PAGE_SIZE);
return min(npages, maxpages);
}
BTW, you've missed iov_iter_gap_alignment()...
next prev parent reply other threads:[~2022-05-22 18:28 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-21 0:46 [RFC] what to do with IOCB_DSYNC? Al Viro
2021-06-21 13:59 ` Christoph Hellwig
2021-06-21 14:03 ` Matthew Wilcox
2021-06-21 14:09 ` Christoph Hellwig
2021-06-21 14:16 ` Matthew Wilcox
2021-06-21 14:22 ` Christoph Hellwig
2021-06-21 14:32 ` Al Viro
2021-06-21 14:35 ` Christoph Hellwig
2021-06-21 15:22 ` Jens Axboe
2022-05-21 17:48 ` Al Viro
2022-05-21 19:03 ` Jens Axboe
2022-05-21 22:14 ` Jens Axboe
2022-05-22 7:45 ` Christoph Hellwig
2022-05-22 10:23 ` Matthew Wilcox
2022-05-22 10:36 ` Al Viro
2022-05-22 11:15 ` Matthew Wilcox
2022-05-22 11:45 ` Christoph Hellwig
2022-05-22 12:39 ` Jens Axboe
2022-05-22 12:48 ` Al Viro
2022-05-22 13:02 ` Jens Axboe
2022-05-22 13:07 ` Al Viro
2022-05-22 13:09 ` Jens Axboe
2022-05-22 18:06 ` Jens Axboe
2022-05-22 18:25 ` Al Viro [this message]
2022-05-22 18:29 ` Jens Axboe
2022-05-22 18:39 ` Al Viro
2022-05-22 18:48 ` Jens Axboe
2022-05-22 19:04 ` Al Viro
2022-05-22 20:03 ` Jens Axboe
2022-05-23 0:42 ` Al Viro
2022-05-23 1:22 ` Jens Axboe
2022-05-23 1:28 ` Jens Axboe
2022-05-23 1:50 ` Jens Axboe
2022-05-23 2:43 ` Jens Axboe
2022-05-23 14:22 ` Al Viro
2022-05-23 14:34 ` Jens Axboe
2022-05-23 14:47 ` Al Viro
2022-05-23 15:12 ` Jens Axboe
2022-05-23 15:44 ` Jens Axboe
2022-05-23 15:49 ` Matthew Wilcox
2022-05-23 15:55 ` Jens Axboe
2022-05-23 16:03 ` Jens Axboe
2022-05-26 14:46 ` Jason A. Donenfeld
2022-05-27 10:09 ` Ingo Molnar
2022-05-27 10:15 ` Jason A. Donenfeld
2022-05-27 14:45 ` Samuel Neves
2022-05-27 10:25 ` Ingo Molnar
2022-05-27 10:36 ` Borislav Petkov
2022-05-28 20:54 ` Sedat Dilek
2022-05-28 20:38 ` Sedat Dilek
2022-05-28 20:39 ` Sedat Dilek
2022-05-23 16:15 ` Al Viro
2022-05-25 14:34 ` Matthew Wilcox
2022-05-26 23:19 ` Al Viro
2022-05-27 14:51 ` Jens Axboe
2022-05-22 12:21 ` Al Viro
2022-05-22 7:43 ` Christoph Hellwig
2022-05-22 12:41 ` Al Viro
2022-05-22 12:51 ` Christoph Hellwig
2021-06-21 14:22 ` Al Viro
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