linux-kernel - Re: [PATCH v12 23/31] mm: don't do swap readahead during speculative page fault

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Message-ID: <20190422213611.GN14666@redhat.com>
Date:   Mon, 22 Apr 2019 17:36:11 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, mhocko@...nel.org, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        aneesh.kumar@...ux.ibm.com, benh@...nel.crashing.org,
        mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        sergey.senozhatsky.work@...il.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, Daniel Jordan <daniel.m.jordan@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Ganesh Mahendran <opensource.ganesh@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Punit Agrawal <punitagrawal@...il.com>,
        vinayak menon <vinayakm.list@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        zhong jiang <zhongjiang@...wei.com>,
        Haiyan Song <haiyanx.song@...el.com>,
        Balbir Singh <bsingharora@...il.com>, sj38.park@...il.com,
        Michel Lespinasse <walken@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com,
        paulmck@...ux.vnet.ibm.com, Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        Vinayak Menon <vinmenon@...eaurora.org>
Subject: Re: [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@...eaurora.org>
> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>

Reviewed-by: Jérôme Glisse <jglisse@...hat.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
>