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SubjectRe: [PATCH v12 23/31] mm: don't do swap readahead during speculative page fault
On Tue, Apr 16, 2019 at 03:45:14PM +0200, Laurent Dufour wrote:
> Vinayak Menon faced a panic because one thread was page faulting a page in
> swap, while another one was mprotecting a part of the VMA leading to a VMA
> split.
> This raise a panic in swap_vma_readahead() because the VMA's boundaries
> were not more matching the faulting address.
>
> To avoid this, if the page is not found in the swap, the speculative page
> fault is aborted to retry a regular page fault.
>
> Reported-by: Vinayak Menon <vinmenon@codeaurora.org>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

Note that you should also skip non swap entry in do_swap_page() when doing
speculative page fault at very least you need to is_device_private_entry()
case.

But this should either be part of patch 22 or another patch to fix swap
case.

> ---
> mm/memory.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 6e6bf61c0e5c..1991da97e2db 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2900,6 +2900,17 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> lru_cache_add_anon(page);
> swap_readpage(page, true);
> }
> + } else if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
> + /*
> + * Don't try readahead during a speculative page fault
> + * as the VMA's boundaries may change in our back.
> + * If the page is not in the swap cache and synchronous
> + * read is disabled, fall back to the regular page
> + * fault mechanism.
> + */
> + delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
> + ret = VM_FAULT_RETRY;
> + goto out;
> } else {
> page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
> vmf);
> --
> 2.21.0
>

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