linux-kernel - Re: [PATCH v4 29/33] x86/mm: try VMA lock-based page fault handling first

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Message-ID: <9a8d788c-b8ba-1b8a-fd79-0e25b1b60bed@kernel.org>
Date:   Fri, 30 Jun 2023 08:35:26 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, mhocko@...e.com, vbabka@...e.cz,
        hannes@...xchg.org, mgorman@...hsingularity.net, dave@...olabs.net,
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        ldufour@...ux.ibm.com, paulmck@...nel.org, mingo@...hat.com,
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        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
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        michalechner92@...glemail.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
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Subject: Re: [PATCH v4 29/33] x86/mm: try VMA lock-based page fault handling
 first

On 29. 06. 23, 17:30, Suren Baghdasaryan wrote:
> On Thu, Jun 29, 2023 at 7:40 AM Jiri Slaby <jirislaby@...nel.org> wrote:
>>
>> Hi,
>>
>> On 27. 02. 23, 18:36, Suren Baghdasaryan wrote:
>>> Attempt VMA lock-based page fault handling first, and fall back to the
>>> existing mmap_lock-based handling if that fails.
>>>
>>> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>>> ---
>>>    arch/x86/Kconfig    |  1 +
>>>    arch/x86/mm/fault.c | 36 ++++++++++++++++++++++++++++++++++++
>>>    2 files changed, 37 insertions(+)
>>>
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index a825bf031f49..df21fba77db1 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -27,6 +27,7 @@ config X86_64
>>>        # Options that are inherently 64-bit kernel only:
>>>        select ARCH_HAS_GIGANTIC_PAGE
>>>        select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
>>> +     select ARCH_SUPPORTS_PER_VMA_LOCK
>>>        select ARCH_USE_CMPXCHG_LOCKREF
>>>        select HAVE_ARCH_SOFT_DIRTY
>>>        select MODULES_USE_ELF_RELA
>>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>>> index a498ae1fbe66..e4399983c50c 100644
>>> --- a/arch/x86/mm/fault.c
>>> +++ b/arch/x86/mm/fault.c
>>> @@ -19,6 +19,7 @@
>>>    #include <linux/uaccess.h>          /* faulthandler_disabled()      */
>>>    #include <linux/efi.h>                      /* efi_crash_gracefully_on_page_fault()*/
>>>    #include <linux/mm_types.h>
>>> +#include <linux/mm.h>                        /* find_and_lock_vma() */
>>>
>>>    #include <asm/cpufeature.h>         /* boot_cpu_has, ...            */
>>>    #include <asm/traps.h>                      /* dotraplinkage, ...           */
>>> @@ -1333,6 +1334,38 @@ void do_user_addr_fault(struct pt_regs *regs,
>>>        }
>>>    #endif
>>>
>>> +#ifdef CONFIG_PER_VMA_LOCK
>>> +     if (!(flags & FAULT_FLAG_USER))
>>> +             goto lock_mmap;
>>> +
>>> +     vma = lock_vma_under_rcu(mm, address);
>>> +     if (!vma)
>>> +             goto lock_mmap;
>>> +
>>> +     if (unlikely(access_error(error_code, vma))) {
>>> +             vma_end_read(vma);
>>> +             goto lock_mmap;
>>> +     }
>>> +     fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
>>> +     vma_end_read(vma);
>>> +
>>> +     if (!(fault & VM_FAULT_RETRY)) {
>>> +             count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
>>> +             goto done;
>>> +     }
>>> +     count_vm_vma_lock_event(VMA_LOCK_RETRY);
>>
>> This is apparently not strong enough as it causes go build failures like:
>>
>> [  409s] strconv
>> [  409s] releasep: m=0x579e2000 m->p=0x5781c600 p->m=0x0 p->status=2
>> [  409s] fatal error: releasep: invalid p state
>> [  409s]
>>
>> [  325s] hash/adler32
>> [  325s] hash/crc32
>> [  325s] cmd/internal/codesign
>> [  336s] fatal error: runtime: out of memory
> 
> Hi Jiri,
> Thanks for reporting! I'm not familiar with go builds. Could you
> please explain the error to me or point me to some documentation to
> decipher that error?

Sorry, we are on the same boat -- me neither. It only popped up in our 
(openSUSE) build system and I only tracked it down by bisection. Let me 
know if I can try something (like a patch or gathering some debug info).

thanks,
-- 
js
suse labs