diff options
Diffstat (limited to 'mm/gup.c')
| -rw-r--r-- | mm/gup.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/mm/gup.c b/mm/gup.c index c7e24301860a..9c6a2f5001c5 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2684,11 +2684,18 @@ static unsigned long lockless_pages_from_mm(unsigned long start, { unsigned long flags; int nr_pinned = 0; + unsigned seq; if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) || !gup_fast_permitted(start, end)) return 0; + if (gup_flags & FOLL_PIN) { + seq = raw_read_seqcount(¤t->mm->write_protect_seq); + if (seq & 1) + return 0; + } + /* * Disable interrupts. The nested form is used, in order to allow full, * general purpose use of this routine. @@ -2703,6 +2710,17 @@ static unsigned long lockless_pages_from_mm(unsigned long start, local_irq_save(flags); gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); local_irq_restore(flags); + + /* + * When pinning pages for DMA there could be a concurrent write protect + * from fork() via copy_page_range(), in this case always fail fast GUP. + */ + if (gup_flags & FOLL_PIN) { + if (read_seqcount_retry(¤t->mm->write_protect_seq, seq)) { + unpin_user_pages(pages, nr_pinned); + return 0; + } + } return nr_pinned; } |