Commit 8daf9c70 authored May 28, 2024 by Oscar Salvador Committed by Andrew Morton Jun 05, 2024

mm/hugetlb: do not call vma_add_reservation upon ENOMEM

sysbot reported a splat [1] on __unmap_hugepage_range().  This is because
vma_needs_reservation() can return -ENOMEM if
allocate_file_region_entries() fails to allocate the file_region struct
for the reservation.

Check for that and do not call vma_add_reservation() if that is the case,
otherwise region_abort() and region_del() will see that we do not have any
file_regions.

If we detect that vma_needs_reservation() returned -ENOMEM, we clear the
hugetlb_restore_reserve flag as if this reservation was still consumed, so
free_huge_folio() will not increment the resv count.

[1] https://lore.kernel.org/linux-mm/0000000000004096100617c58d54@google.com/T/#ma5983bc1ab18a54910da83416b3f89f3c7ee43aa

Link: https://lkml.kernel.org/r/20240528205323.20439-1-osalvador@suse.de


Fixes: df7a6d1f ("mm/hugetlb: restore the reservation if needed")
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reported-and-tested-by:  <syzbot+d3fe2dc5ffe9380b714b@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-mm/0000000000004096100617c58d54@google.com/


Cc: Breno Leitao <leitao@debian.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent c2dc78b8

mm/hugetlb.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -5768,8 +5768,20 @@ void __unmap_hugepage_range(struct mmu_gather tlb, struct vm_area_struct vma,
		* do_exit() will not see it, and will keep the reservation
		* forever.
		*/
		if (adjust_reservation && vma_needs_reservation(h, vma, address))
		if (adjust_reservation) {
		int rc = vma_needs_reservation(h, vma, address);

		if (rc < 0)
		/* Pressumably allocate_file_region_entries failed
		* to allocate a file_region struct. Clear
		* hugetlb_restore_reserve so that global reserve
		* count will not be incremented by free_huge_folio.
		* Act as if we consumed the reservation.
		*/
		folio_clear_hugetlb_restore_reserve(page_folio(page));
		else if (rc)
		vma_add_reservation(h, vma, address);
		}

		tlb_remove_page_size(tlb, page, huge_page_size(h));
		/*