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    SubjectRe: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal
    On Wed, Apr 08, 2020 at 04:30:24PM +0200, Michal Hocko wrote:
    > On Wed 08-04-20 10:20:39, Peter Xu wrote:
    > > On Wed, Apr 08, 2020 at 12:21:28PM +0200, Michal Hocko wrote:
    > > > On Tue 07-04-20 21:40:09, Peter Xu wrote:
    > > > > lookup_node() uses gup to pin the page and get node information. It
    > > > > checks against ret>=0 assuming the page will be filled in. However
    > > > > it's also possible that gup will return zero, for example, when the
    > > > > thread is quickly killed with a fatal signal. Teach lookup_node() to
    > > > > gracefully return an error -EFAULT if it happens.
    > > > >
    > > > > Meanwhile, initialize "page" to NULL to avoid potential risk of
    > > > > exploiting the pointer.
    > > > >
    > > > > Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com
    > > > > Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
    > > >
    > > > I am not familiar with thic commit but shouldn't gup return ERESTARTSYS
    > > > on a fatal signal?
    > >
    > > Hi, Michal,
    > >
    > > I do see quite a few usages on -ERESTARTSYS, but also some others,
    > > majorly -EINTR, or even -EFAULT. I think it could be a more general
    > > question rather than a specific question to this patch only.
    >
    > I am sorry but I was probably not clear enough. I was mostly worried
    > that gup doesn't return ERESTARTSYS or EINTR when it backed off because
    > of fatal signal pending. Your patch is checking for 0 an indicating that
    > this is that condition.

    Yeah I just noticed the fact, sorry!

    Hillf just posted a fix there for recovering the behavior:

    https://lore.kernel.org/lkml/20200408151213.GE66033@xz-x1/

    Thanks,

    --
    Peter Xu

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