On 06.09.25 01:00, Eric Biggers wrote:
On Fri, Sep 05, 2025 at 08:41:23AM +0200, David Hildenbrand wrote:
On 01.09.25 17:03, David Hildenbrand wrote:
We can just cleanup the code by calculating the #refs earlier, so we can just inline what remains of record_subpages().
Calculate the number of references/pages ahead of times, and record them only once all our tests passed.
Signed-off-by: David Hildenbrand david@redhat.com
mm/gup.c | 25 ++++++++----------------- 1 file changed, 8 insertions(+), 17 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c index c10cd969c1a3b..f0f4d1a68e094 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -484,19 +484,6 @@ static inline void mm_set_has_pinned_flag(struct mm_struct *mm) #ifdef CONFIG_MMU #ifdef CONFIG_HAVE_GUP_FAST -static int record_subpages(struct page *page, unsigned long sz,
unsigned long addr, unsigned long end,struct page **pages)-{
- int nr;
- page += (addr & (sz - 1)) >> PAGE_SHIFT;
- for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
pages[nr] = page++;- return nr;
-}
- /**
- try_grab_folio_fast() - Attempt to get or pin a folio in fast path.
- @page: pointer to page to be grabbed
@@ -2967,8 +2954,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, if (pmd_special(orig)) return 0;
- page = pmd_page(orig);
- refs = record_subpages(page, PMD_SIZE, addr, end, pages + *nr);
- refs = (end - addr) >> PAGE_SHIFT;
- page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); folio = try_grab_folio_fast(page, refs, flags); if (!folio)
@@ -2989,6 +2976,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, } *nr += refs;
- for (; refs; refs--)
*(pages++) = page++;@@ -3007,8 +2996,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr, if (pud_special(orig)) return 0;
- page = pud_page(orig);
- refs = record_subpages(page, PUD_SIZE, addr, end, pages + *nr);
- refs = (end - addr) >> PAGE_SHIFT;
- page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); folio = try_grab_folio_fast(page, refs, flags); if (!folio)
@@ -3030,6 +3019,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr, } *nr += refs;
- for (; refs; refs--)
*(pages++) = page++;Okay, this code is nasty. We should rework this code to just return the nr and receive a the proper pages pointer, getting rid of the "*nr" parameter.
For the time being, the following should do the trick:
commit bfd07c995814354f6b66c5b6a72e96a7aa9fb73b (HEAD -> nth_page) Author: David Hildenbrand david@redhat.com Date: Fri Sep 5 08:38:43 2025 +0200
fixup: mm/gup: remove record_subpages() pages is not adjusted by the caller, but idnexed by existing *nr. Signed-off-by: David Hildenbrand <david@redhat.com>diff --git a/mm/gup.c b/mm/gup.c index 010fe56f6e132..22420f2069ee1 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2981,6 +2981,7 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0; }
pages += *nr; *nr += refs; for (; refs; refs--) *(pages++) = page++;@@ -3024,6 +3025,7 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr, return 0; }
pages += *nr; *nr += refs; for (; refs; refs--) *(pages++) = page++;Can this get folded in soon? This bug is causing crashes in AF_ALG too.
Andrew immediately dropped the original patch, so it's gone from mm-unstable and should be gone from next soon (today?).