On Mon, Dec 9, 2024 at 11:52 AM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
>
> On Mon, Dec 9, 2024 at 10:47 AM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
> >
> > On Mon, Dec 9, 2024 at 9:07 AM Malte Schröder <malte.schroeder@xxxxxxxx> wrote:
> > >
> > > On 09/12/2024 16:48, Josef Bacik wrote:
> > > > On Mon, Dec 09, 2024 at 03:28:14PM +0000, Matthew Wilcox wrote:
> > > >> On Mon, Dec 09, 2024 at 09:49:48AM -0500, Josef Bacik wrote:
> > > >>>> Ha! This time I bisected from f03b296e8b51 to d1dfb5f52ffc. I ended up
> > > >>>> with 3b97c3652d91 as the culprit.
> > > >>> Willy, I've looked at this code and it does indeed look like a 1:1 conversion,
> > > >>> EXCEPT I'm fuzzy about how how this works with large folios. Previously, if we
> > > >>> got a hugepage in, we'd get each individual struct page back for the whole range
> > > >>> of the hugepage, so if for example we had a 2M hugepage, we'd fill in the
> > > >>> ->offset for each "middle" struct page as 0, since obviously we're consuming
> > > >>> PAGE_SIZE chunks at a time.
> > > >>>
> > > >>> But now we're doing this
> > > >>>
> > > >>> for (i = 0; i < nfolios; i++)
> > > >>> ap->folios[i + ap->num_folios] = page_folio(pages[i]);
> > > >>>
> > > >>> So if userspace handed us a 2M hugepage, page_folio() on each of the
> > > >>> intermediary struct page's would return the same folio, correct? So we'd end up
> > > >>> with the wrong offsets for our fuse request, because they should be based from
> > > >>> the start of the folio, correct?
> > > >> I think you're 100% right. We could put in some nice asserts to check
> > > >> this is what's happening, but it does seem like a rather incautious
> > > >> conversion. Yes, all folios _in the page cache_ for fuse are small, but
> > > >> that's not guaranteed to be the case for folios found in userspace for
> > > >> directio. At least the comment is wrong, and I'd suggest the code is too.
> > > > Ok cool, Malte can you try the attached only compile tested patch and see if the
> > > > problem goes away? Thanks,
> > > >
> > > > Josef
> > > >
> > > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > > > index 88d0946b5bc9..c4b93ead99a5 100644
> > > > --- a/fs/fuse/file.c
> > > > +++ b/fs/fuse/file.c
> > > > @@ -1562,9 +1562,19 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
> > > > nfolios = DIV_ROUND_UP(ret, PAGE_SIZE);
> > > >
> > > > ap->descs[ap->num_folios].offset = start;
> > > > - fuse_folio_descs_length_init(ap->descs, ap->num_folios, nfolios);
> > > > - for (i = 0; i < nfolios; i++)
> > > > - ap->folios[i + ap->num_folios] = page_folio(pages[i]);
> > > > + for (i = 0; i < nfolios; i++) {
> > > > + struct folio *folio = page_folio(pages[i]);
> > > > + unsigned int offset = start +
> > > > + (folio_page_idx(folio, pages[i]) << PAGE_SHIFT);
> > > > + unsigned int len = min_t(unsigned int, ret, folio_size(folio) - offset);
> > > > +
> > > > + len = min_t(unsigned int, len, PAGE_SIZE);
> > > > +
> > > > + ap->descs[ap->num_folios + i].offset = offset;
> > > > + ap->descs[ap->num_folios + i].length = len;
> > > > + ap->folios[i + ap->num_folios] = folio;
> > > > + start = 0;
> > > > + }
> > > >
> > > > ap->num_folios += nfolios;
> > > > ap->descs[ap->num_folios - 1].length -=
> > >
> > > The problem persists with this patch.
> > >
>
> Malte, could you try Josef's patch except with that last line
> "ap->descs[ap->num_pages - 1].length -= (PAGE_SIZE - ret) &
> (PAGE_SIZE - 1);" also removed? I think we need that line removed as
> well since that does a "-=" instead of a "=" and
> ap->descs[ap->num_folios - 1].length gets set inside the for loop.
>
> In the meantime, I'll try to get a local repro running on fsx so that
> you don't have to keep testing out repos for us.
I was able to repro this locally by doing:
-- start libfuse server --
sudo ./libfuse/build/example/passthrough_hp --direct-io ~/src ~/fuse_mount
-- patch + compile this (rough / ugly-for-now) code snippet --
diff --git a/ltp/fsx.c b/ltp/fsx.c
index 777ba0de..9f040bc4 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -1049,7 +1049,8 @@ dowrite(unsigned offset, unsigned size)
}
}
-
+#define TWO_MIB (1 << 21) // 2 MiB in bytes
void
domapwrite(unsigned offset, unsigned size)
{
@@ -1057,6 +1058,8 @@ domapwrite(unsigned offset, unsigned size)
unsigned map_size;
off_t cur_filesize;
char *p;
+ int ret;
+ unsigned size_2mib_aligned;
offset -= offset % writebdy;
if (size == 0) {
@@ -1101,6 +1104,41 @@ domapwrite(unsigned offset, unsigned size)
pg_offset = offset & PAGE_MASK;
map_size = pg_offset + size;
+ size_2mib_aligned = (size + TWO_MIB - 1) & ~(TWO_MIB - 1);
+ void *placeholder_map = mmap(NULL, size_2mib_aligned * 2, PROT_NONE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!placeholder_map) {
+ prterr("domapwrite: placeholder map");
+ exit(202);
+ }
+
+ /* align address to nearest 2 MiB */
+ void *aligned_address =
+ (void *)(((uintptr_t)placeholder_map + TWO_MIB - 1) &
~(TWO_MIB - 1));
+
+ void *map = mmap(aligned_address, size_2mib_aligned, PROT_READ
| PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED |
MAP_POPULATE, -1, 0);
+
+ ret = madvise(map, size_2mib_aligned, MADV_COLLAPSE);
+ if (ret) {
+ prterr("domapwrite: madvise collapse");
+ exit(203);
+ }
+
+ memcpy(map, good_buf + offset, size);
+
+ if (lseek(fd, offset, SEEK_SET) == -1) {
+ prterr("domapwrite: lseek");
+ exit(204);
+ }
+
+ ret = write(fd, map, size);
+ if (ret == -1) {
+ prterr("domapwrite: write");
+ exit(205);
+ }
+
+ /*
if ((p = (char *)mmap(0, map_size, PROT_READ | PROT_WRITE,
MAP_FILE | MAP_SHARED, fd,
(off_t)(offset - pg_offset))) == (char *)-1) {
@@ -1119,6 +1157,15 @@ domapwrite(unsigned offset, unsigned size)
prterr("domapwrite: munmap");
report_failure(204);
}
+ */
+ if (munmap(map, size_2mib_aligned) != 0) {
+ prterr("domapwrite: munmap map");
+ report_failure(206);
+ }
+ if (munmap(placeholder_map, size_2mib_aligned * 2) != 0) {
+ prterr("domapwrite: munmap placeholder_map");
+ report_failure(207);
+ }
}
-- run fsx test --
sudo ./fsx -b 3 ~/fuse_mount/example.txt -N 5000
On the offending commit 3b97c3652, I'm seeing:
[user]$ sudo ./fsx -b 3 ~/fuse_mount/example.txt -N 5000
Will begin at operation 3
Seed set to 1
...
READ BAD DATA: offset = 0x1925f, size = 0xf7a3, fname =
/home/user/fuse_mount/example.txt
OFFSET GOOD BAD RANGE
0x1e43f 0x4b4a 0x114a 0x0
operation# (mod 256) for the bad data may be 74
0x1e441 0xa64a 0xeb4a 0x1
operation# (mod 256) for the bad data may be 74
0x1e443 0x264a 0xe44a 0x2
operation# (mod 256) for the bad data may be 74
0x1e445 0x254a 0x9e4a 0x3
...
Correct content saved for comparison
(maybe hexdump "/home/user/fuse_mount/example.txt" vs
"/home/user/fuse_mount/example.txt.fsxgood")
I tested Josef's patch with the "ap->descs[ap->num_pages - 1].length
-= (PAGE_SIZE - ret) & (PAGE_SIZE - 1);" line removed and it fixed the
issue:
[user]$ sudo ./fsx -b 3 ~/fuse_mount/example.txt -N 5000
Will begin at operation 3
Seed set to 1
...
copying to largest ever: 0x3e19b
copying to largest ever: 0x3e343
fallocating to largest ever: 0x40000
All 5000 operations completed A-OK!
Malte, would you mind double-checking whether this fixes the issue
you're seeing on your end?
Thanks,
Joanne
>
> Thanks,
> Joanne
> >
> > Catching up on this thread now. I'll investigate this today.
> >
> > >
> > > /Malte
> > >
