From: Andrew Morton <akpm@linux-foundation.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
qemu-devel@nongnu.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/1] mm: gup: teach get_user_pages_unlocked to handle FOLL_NOWAIT
Date: Fri, 2 Mar 2018 11:39:56 -0800 [thread overview]
Message-ID: <20180302113956.0c0763f6c7cd47e104a59118@linux-foundation.org> (raw)
In-Reply-To: <20180302174343.5421-2-aarcange@redhat.com>
On Fri, 2 Mar 2018 18:43:43 +0100 Andrea Arcangeli <aarcange@redhat.com> wrote:
> KVM is hanging during postcopy live migration with userfaultfd because
> get_user_pages_unlocked is not capable to handle FOLL_NOWAIT.
>
> Earlier FOLL_NOWAIT was only ever passed to get_user_pages.
>
> Specifically faultin_page (the callee of get_user_pages_unlocked
> caller) doesn't know that if FAULT_FLAG_RETRY_NOWAIT was set in the
> page fault flags, when VM_FAULT_RETRY is returned, the mmap_sem wasn't
> actually released (even if nonblocking is not NULL). So it sets
> *nonblocking to zero and the caller won't release the mmap_sem
> thinking it was already released, but it wasn't because of
> FOLL_NOWAIT.
>
> Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
I added
Fixes: ce53053ce378c ("kvm: switch get_user_page_nowait() to get_user_pages_unlocked()")
Cc: <stable@vger.kernel.org>
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prev parent reply other threads:[~2018-03-02 19:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-02 17:43 [PATCH 0/1] FOLL_NOWAIT and get_user_pages_unlocked Andrea Arcangeli
2018-03-02 17:43 ` [PATCH 1/1] mm: gup: teach get_user_pages_unlocked to handle FOLL_NOWAIT Andrea Arcangeli
2018-03-02 19:39 ` Andrew Morton [this message]
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