Commit d9c1ddf3 authored by Qi Zheng's avatar Qi Zheng Committed by Andrew Morton
Browse files

mm: handle_pte_fault() use pte_offset_map_rw_nolock() 

In handle_pte_fault(), we may modify the vmf->pte after acquiring the
vmf->ptl, so convert it to using pte_offset_map_rw_nolock().  But since we
will do the pte_same() check, so there is no need to get pmdval to do
pmd_same() check, just pass a dummy variable to it.

Link: https://lkml.kernel.org/r/af8d694853b44c5a6018403ae435440e275854c7.1727332572.git.zhengqi.arch@bytedance.com


Signed-off-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarMuchun Song <muchun.song@linux.dev>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent fc9c45b7

mm/memory.c

+12 −2
Original line number Diff line number Diff line
@@ -5742,14 +5742,24 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) 
		vmf->pte = NULL;

		vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID;

	} else {

		pmd_t dummy_pmdval;



		/*

		 * A regular pmd is established and it can't morph into a huge

		 * pmd by anon khugepaged, since that takes mmap_lock in write

		 * mode; but shmem or file collapse to THP could still morph

		 * it into a huge pmd: just retry later if so.

		 *

		 * Use the maywrite version to indicate that vmf->pte may be

		 * modified, but since we will use pte_same() to detect the

		 * change of the !pte_none() entry, there is no need to recheck

		 * the pmdval. Here we chooes to pass a dummy variable instead

		 * of NULL, which helps new user think about why this place is

		 * special.

		 */

		vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,

						 vmf->address, &vmf->ptl);

		vmf->pte = pte_offset_map_rw_nolock(vmf->vma->vm_mm, vmf->pmd,

						    vmf->address, &dummy_pmdval,

						    &vmf->ptl);

		if (unlikely(!vmf->pte))

			return 0;

		vmf->orig_pte = ptep_get_lockless(vmf->pte);