Lord above.
Also semantics of 'if bytes == 0, then check first page anyway' which you do
capture.
Yeah, I think bytes == 0 would not make any sense, though. Staring
briefly at the single caller, that seems to be the case (bytes != 0).
OK think I have convinced myself this is right, so hopefully no deeply subtle
off-by-one issues here :P
Anyway, LGTM, so:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
---
fs/hugetlbfs/inode.c | 33 +++++++++++----------------------
1 file changed, 11 insertions(+), 22 deletions(-)
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index c5a46d10afaa0..6ca1f6b45c1e5 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -198,31 +198,20 @@ hugetlb_get_unmapped_area(struct file *file, unsigned
long addr,
static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
size_t bytes)
{
- struct page *page;
- size_t n = 0;
- size_t res = 0;
-
- /* First page to start the loop. */
- page = folio_page(folio, offset / PAGE_SIZE);
- offset %= PAGE_SIZE;
- while (1) {
- if (is_raw_hwpoison_page_in_hugepage(page))
- break;
+ struct page *page = folio_page(folio, offset / PAGE_SIZE);
+ size_t safe_bytes;
+
+ if (is_raw_hwpoison_page_in_hugepage(page))
+ return 0;
+ /* Safe to read the remaining bytes in this page. */
+ safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
+ page++;
- /* Safe to read n bytes without touching HWPOISON subpage. */
- n = min(bytes, (size_t)PAGE_SIZE - offset);
- res += n;
- bytes -= n;
- if (!bytes || !n)
+ for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
OK this is quite subtle - so if safe_bytes == bytes, this means we've confirmed
that all requested bytes are safe.
So offset=0, bytes = 4096 would fail this (as safe_bytes == 4096).
Maybe worth putting something like:
/*
* Now we check page-by-page in the folio to see if any bytes we don't
* yet know to be safe are contained within posioned pages or not.
*/
Above the loop. Or something like this.
"Check each remaining page as long as we are not done yet."
+ if (is_raw_hwpoison_page_in_hugepage(page))
break;
- offset += n;
- if (offset == PAGE_SIZE) {
- page++;
- offset = 0;
- }
- }
- return res;
+ return min(safe_bytes, bytes);
Yeah given above analysis this seems correct.
You must have torn your hair out over this :)
I could resist the urge to clean that up, yes.
I'll also drop the "The implementation borrows the iteration logic from
copy_page_to_iter*." part, because I suspect this comment no longer
makes sense.
Thanks!
--
Cheers
David / dhildenb
