diff options
| -rw-r--r-- | fs/aio.c | 15 |
1 files changed, 12 insertions, 3 deletions
@@ -307,16 +307,25 @@ static int aio_setup_ring(struct kioctx *ctx) aio_free_ring(ctx); return -EAGAIN; } - up_write(&mm->mmap_sem); - - mm_populate(ctx->mmap_base, populate); pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base); + + /* We must do this while still holding mmap_sem for write, as we + * need to be protected against userspace attempting to mremap() + * or munmap() the ring buffer. + */ ctx->nr_pages = get_user_pages(current, mm, ctx->mmap_base, nr_pages, 1, 0, ctx->ring_pages, NULL); + + /* Dropping the reference here is safe as the page cache will hold + * onto the pages for us. It is also required so that page migration + * can unmap the pages and get the right reference count. + */ for (i = 0; i < ctx->nr_pages; i++) put_page(ctx->ring_pages[i]); + up_write(&mm->mmap_sem); + if (unlikely(ctx->nr_pages != nr_pages)) { aio_free_ring(ctx); return -EAGAIN; |