From: Finn Thain <fthain@linux-m68k.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-arch@vger.kernel.org, linux-alpha@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-hexagon@vger.kernel.org,
linux-m68k@lists.linux-m68k.org, Michal Simek <monstr@monstr.eu>,
Dinh Nguyen <dinguyen@kernel.org>,
openrisc@lists.librecores.org, linux-parisc@vger.kernel.org,
linux-riscv@lists.infradead.org, sparclinux@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 04/10] m68k: fix livelock in uaccess
Date: Sun, 5 Feb 2023 17:18:08 +1100 (AEDT) [thread overview]
Message-ID: <92a4aa45-0a7c-a389-798a-2f3e3cfa516f@linux-m68k.org> (raw)
In-Reply-To: <Y9l0aBPUEpf1bci9@ZenIV>
Hello Al,
On Tue, 31 Jan 2023, Al Viro wrote:
> m68k equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY
> handling" If e.g. get_user() triggers a page fault and a fatal signal is
> caught, we might end up with handle_mm_fault() returning VM_FAULT_RETRY
> and not doing anything to page tables. In such case we must *not*
> return to the faulting insn - that would repeat the entire thing without
> making any progress; what we need instead is to treat that as failed
> (user) memory access.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
That could be a bug I was chasing back in 2021 but never found. The mmap
stressors in stress-ng were triggering a crash on a Mac Quadras, though
only rarely. Sometimes it would run all day without a failure.
Last year when I started using GCC 12 to build the kernel, I saw the same
workload fail again but the failure mode had become a silent hang/livelock
instead of the oopses I got with GCC 6.
When I press the NMI button after the livelock I always see
do_page_fault() in the backtrace. So I've been testing your patch. I've
been running the same stress-ng reproducer for about 12 hours now with no
failures which looks promising.
In case that stress-ng testing is of use:
Tested-by: Finn Thain <fthain@linux-m68k.org>
BTW, how did you identify that bug in do_page_fault()? If its the same bug
I was chasing, it could be an old one. The stress-ng logs I collected last
year include a crash from a v4.14 build.
> ---
> arch/m68k/mm/fault.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
> index 4d2837eb3e2a..228128e45c67 100644
> --- a/arch/m68k/mm/fault.c
> +++ b/arch/m68k/mm/fault.c
> @@ -138,8 +138,11 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> fault = handle_mm_fault(vma, address, flags, regs);
> pr_debug("handle_mm_fault returns %x\n", fault);
>
> - if (fault_signal_pending(fault, regs))
> + if (fault_signal_pending(fault, regs)) {
> + if (!user_mode(regs))
> + goto no_context;
> return 0;
> + }
>
> /* The fault is fully completed (including releasing mmap lock) */
> if (fault & VM_FAULT_COMPLETED)
>
next prev parent reply other threads:[~2023-02-05 6:16 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-31 20:02 [RFC][PATCHSET] VM_FAULT_RETRY fixes Al Viro
2023-01-31 20:03 ` [PATCH 01/10] alpha: fix livelock in uaccess Al Viro
2023-03-07 0:48 ` patchwork-bot+linux-riscv
2023-01-31 20:03 ` [PATCH 02/10] hexagon: " Al Viro
2023-02-10 2:59 ` Brian Cain
2023-01-31 20:04 ` [PATCH 03/10] ia64: " Al Viro
2023-01-31 20:04 ` [PATCH 04/10] m68k: " Al Viro
2023-02-05 6:18 ` Finn Thain [this message]
2023-02-05 18:51 ` Linus Torvalds
2023-02-07 3:07 ` Finn Thain
2023-02-05 20:39 ` Al Viro
2023-02-05 20:41 ` Linus Torvalds
2023-02-06 12:08 ` Geert Uytterhoeven
2023-01-31 20:05 ` [PATCH 05/10] microblaze: " Al Viro
2023-01-31 20:05 ` [PATCH 06/10] nios2: " Al Viro
2023-01-31 20:06 ` [PATCH 07/10] openrisc: " Al Viro
2023-01-31 20:06 ` [PATCH 08/10] parisc: " Al Viro
2023-02-06 16:58 ` Helge Deller
2023-02-28 17:34 ` Al Viro
2023-02-28 15:22 ` Guenter Roeck
2023-02-28 19:18 ` Michael Schmitz
2023-01-31 20:06 ` [PATCH 09/10] riscv: " Al Viro
2023-02-06 20:06 ` Björn Töpel
2023-02-07 16:11 ` Geert Uytterhoeven
2023-01-31 20:07 ` [PATCH 10/10] sparc: " Al Viro
2023-01-31 20:24 ` [RFC][PATCHSET] VM_FAULT_RETRY fixes Linus Torvalds
2023-01-31 21:10 ` Al Viro
2023-01-31 21:19 ` Linus Torvalds
2023-01-31 21:49 ` Al Viro
2023-02-01 0:00 ` Linus Torvalds
2023-02-01 19:48 ` Peter Xu
2023-02-01 22:18 ` Al Viro
2023-02-02 0:57 ` Al Viro
2023-02-02 22:56 ` Peter Xu
2023-02-04 0:26 ` Al Viro
2023-02-05 5:10 ` Al Viro
2023-02-01 8:21 ` Helge Deller
2023-02-01 19:51 ` Linus Torvalds
2023-02-01 10:50 ` Mark Rutland
2023-02-06 12:08 ` Geert Uytterhoeven
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