From: Pavel Machek <pavel@ucw.cz>
To: Hugh Dickins <hughd@google.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Andrea Arcangeli <aarcange@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults
Date: Sun, 26 May 2019 19:25:09 +0200 [thread overview]
Message-ID: <20190526172509.GC1282@xo-6d-61-c0.localdomain> (raw)
In-Reply-To: <alpine.LSU.2.11.1905241429460.1141@eggly.anvils>
On Fri 2019-05-24 15:22:51, Hugh Dickins wrote:
> On Wed, 22 May 2019, Sebastian Andrzej Siewior wrote:
> > On 2019-05-22 12:21:13 [-0700], Andrew Morton wrote:
> > > On Tue, 14 May 2019 17:29:55 +0300 Mike Rapoport <rppt@linux.ibm.com> wrote:
> > >
> > > > When get_user_pages*() is called with pages = NULL, the processing of
> > > > VM_FAULT_RETRY terminates early without actually retrying to fault-in all
> > > > the pages.
> > > >
> > > > If the pages in the requested range belong to a VMA that has userfaultfd
> > > > registered, handle_userfault() returns VM_FAULT_RETRY *after* user space
> > > > has populated the page, but for the gup pre-fault case there's no actual
> > > > retry and the caller will get no pages although they are present.
> > > >
> > > > This issue was uncovered when running post-copy memory restore in CRIU
> > > > after commit d9c9ce34ed5c ("x86/fpu: Fault-in user stack if
> > > > copy_fpstate_to_sigframe() fails").
>
> I've been getting unexplained segmentation violations, and "make" giving
> up early, when running kernel builds under swapping memory pressure: no
> CRIU involved.
>
> Bisected last night to that same x86/fpu commit, not itself guilty, but
> suffering from the odd behavior of get_user_pages_unlocked() giving up
> too early.
>
> (I wondered at first if copy_fpstate_to_sigframe() ought to retry if
> non-negative ret < nr_pages, but no, that would be wrong: a present page
> followed by an invalid area would repeatedly return 1 for nr_pages 2.)
>
> Cc'ing Pavel, who's been having segfault trouble in emacs: maybe same?
The emacs segfault was always during process exit. This sounds different...
I don't see problems with make.
But its true that at least one of affected machines uses swap heavily.
Best regards,
Pavel
next prev parent reply other threads:[~2019-05-26 17:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-26 17:33 [PATCH] x86/fpu: Use fault_in_pages_writeable() for pre-faulting Sebastian Andrzej Siewior
2019-05-26 17:35 ` Sebastian Andrzej Siewior
2019-05-26 19:25 ` Hugh Dickins
2019-05-28 11:54 ` My emacs problem -- was " Pavel Machek
2019-05-29 4:18 ` Andrew Morton
2019-05-29 7:25 ` [PATCH v2] " Sebastian Andrzej Siewior
2019-05-14 14:29 ` [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults Mike Rapoport
2019-05-16 16:25 ` Andrei Vagin
2019-05-21 15:53 ` Mike Rapoport
2019-05-22 19:21 ` Andrew Morton
2019-05-22 19:43 ` Sebastian Andrzej Siewior
2019-05-24 22:22 ` Hugh Dickins
2019-05-25 8:45 ` Sebastian Andrzej Siewior
2019-05-25 18:09 ` Hugh Dickins
2019-05-26 19:36 ` Sebastian Andrzej Siewior
2019-05-26 20:17 ` Hugh Dickins
2019-05-26 17:25 ` Pavel Machek [this message]
2019-05-22 20:38 ` Mike Rapoport
2019-05-22 21:18 ` Andrew Morton
2019-06-22 17:51 ` Andrea Arcangeli
2019-06-06 17:25 ` [tip:x86/urgent] x86/fpu: Use fault_in_pages_writeable() for pre-faulting tip-bot for Hugh Dickins
2019-05-29 21:29 ` [PATCH v2] " Chris Wilson
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