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Date:   Mon, 3 Jul 2023 19:25:03 -0700
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Subject: Re: [PATCH 3/4] mm/memory: convert do_shared_fault() to folios
Content-Language: en-US
To:     SeongJae Park <sj@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, willy@infradead.org
References: <20230703220559.1360-1-sj@kernel.org>
From:   Sidhartha Kumar <sidhartha.kumar@oracle.com>
In-Reply-To: <20230703220559.1360-1-sj@kernel.org>
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On 7/3/23 3:05 PM, SeongJae Park wrote:
> Hi Sidharta,
> 
> On Sun, 2 Jul 2023 22:58:49 -0700 Sidhartha Kumar <sidhartha.kumar@oracle.com> wrote:
> 
>> Saves three implicit calls to compound_head().
>>
>> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
>> ---
>>   mm/memory.c | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 93480e846ace6..33bf13431974c 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4594,6 +4594,7 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>>   {
>>   	struct vm_area_struct *vma = vmf->vma;
>>   	vm_fault_t ret, tmp;
>> +	struct folio *folio = page_folio(vmf->page);
>>   
>>   	ret = __do_fault(vmf);
>>   	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
>> @@ -4604,11 +4605,11 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>>   	 * about to become writable
>>   	 */
>>   	if (vma->vm_ops->page_mkwrite) {
>> -		unlock_page(vmf->page);
>> +		folio_unlock(folio);
>>   		tmp = do_page_mkwrite(vmf);
>>   		if (unlikely(!tmp ||
>>   				(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
>> -			put_page(vmf->page);
>> +			folio_put(folio);
>>   			return tmp;
>>   		}
>>   	}
>> @@ -4616,8 +4617,8 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>>   	ret |= finish_fault(vmf);
>>   	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
>>   					VM_FAULT_RETRY))) {
>> -		unlock_page(vmf->page);
>> -		put_page(vmf->page);
>> +		folio_unlock(folio);
>> +		folio_put(folio);
>>   		return ret;
>>   	}
> 
> I found the latest mm-unstable tree fails booting with stacktraces like below,
> and bisecting points this patch (commit a43f078c7a3b of mm-unstable).  Do you
> have any idea?

This looks like the issue that Matthew pointed out in the thread.
Andrew, can you please remove this patch series.

Thanks
Sidhartha Kumar
> 
> [    7.388551] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [    7.389149] systemd[1]: Starting Load Kernel Module pstore_zone...
> [    7.390101] #PF: supervisor read access in kernel mode
> [    7.392370] #PF: error_code(0x0000) - not-present page
> [    7.392372] PGD 0 P4D 0
> [    7.392376] Oops: 0000 [#1] PREEMPT SMP PTI
> [    7.392379] CPU: 9 PID: 594 Comm: systemd-journal Not tainted 6.4.0+ #8
> [         S7t.a3r9t2i3n82] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-4
> [    7.392384] RIP: 0010:_compound_head (include/linux/page-flags.h:245)
> [ 7.400935] Code: e8 35 b5 cd ff 5d c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 90f
> 
> Code starting with the faulting instruction
> ===========================================
>     0:   e8 35 b5 cd ff          callq  0xffffffffffcdb53a
>     5:   5d                      pop    %rbp
>     6:   c3                      retq
>     7:   cc                      int3
>     8:   cc                      int3
>     9:   cc                      int3
>     a:   cc                      int3
>     b:   66 66 2e 0f 1f 84 00    data16 nopw %cs:0x0(%rax,%rax,1)
>    12:   00 00 00 00
>    16:   0f 1f 40 00             nopl   0x0(%rax)
>    1a:   90                      nop
>    1b:   0f                      .byte 0xf
> [    7.405283] RSP: 0000:ffffb86140cd3d58 EFLAGS: 00010202
> [    7.406551] RAX: ffff96d3c19c4d38 RBX: ffffffffa103f080 RCX: 00000001019c4067
> [    7.408233] RDX: 0000000000000000 RSI: ffff96d2c0000d38 RDI: 0000000000000000
> [    7.409893] RBP: ffffb86140cd3d90 R08: ffff96d3c19c4d38 R09: 0000000000000067
> [    7.411457] R10: 0000000000000000 R11: 00007f2ae19d5fff R12: ffffb86140cd3dd0
> [    7.412792] R13: 0000000000000001 R14: ffff96d3cb7aa450 R15: 0000000000000860
> [    7.414139] FS:  00007f2ae0f40980(0000) GS:ffff96f1fd640000(0000) knlGS:0000000000000000
> [    7.415699] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    7.416780] CR2: 0000000000000008 CR3: 0000000104830000 CR4: 00000000000006e0
> [    7.418115] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    7.419492] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [    7.420830] Call Trace:
> [    7.421308]  <TASK>
> [    7.421722] ? show_regs (arch/x86/kernel/dumpstack.c:479)
> [    7.422411] ? __die_body (arch/x86/kernel/dumpstack.c:421)
> [    7.423113] ? __die (arch/x86/kernel/dumpstack.c:435)
> [    7.423716] ? page_fault_oops (arch/x86/mm/fault.c:707)
> [    7.424504] ? search_bpf_extables (kernel/bpf/core.c:751)
> [    7.425329] ? __pfx__compound_head (include/linux/page-flags.h:245)
> [    7.426171] ? search_exception_tables (kernel/extable.c:64)
> [    7.427084] ? kernelmode_fixup_or_oops (arch/x86/mm/fault.c:762)
> [    7.427995] ? __bad_area_nosemaphore (arch/x86/mm/fault.c:860)
> [    7.428891] ? up_read (arch/x86/include/asm/preempt.h:104 kernel/locking/rwsem.c:1354 kernel/locking/rwsem.c:1616)
> [    7.429514] ? bad_area_nosemaphore (arch/x86/mm/fault.c:867)
> [    7.430367] ? do_user_addr_fault (arch/x86/mm/fault.c:1458)
> [    7.431238] ? exc_page_fault (arch/x86/include/asm/paravirt.h:695 arch/x86/mm/fault.c:1495 arch/x86/mm/fault.c:1543)
> [    7.431998] ? asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570)
> [    7.432802] ? __pfx__compound_head (include/linux/page-flags.h:245)
> [    7.433640] ? do_pte_missing (mm/memory.c:4610 mm/memory.c:4682 mm/memory.c:3670)
> [    7.434425] __handle_mm_fault (mm/memory.c:4947 mm/memory.c:5087)
> [    7.435234] handle_mm_fault (mm/memory.c:5252)
> [    7.435976] do_user_addr_fault (arch/x86/mm/fault.c:1393)
> [    7.436786] exc_page_fault (arch/x86/include/asm/paravirt.h:695 arch/x86/mm/fault.c:1495 arch/x86/mm/fault.c:1543)
> [    7.437517] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570)
> [    7.438294] RIP: 0033:0x7f2ae1480ace
> [ 7.439035] Code: 8d a0 48 00 00 00 49 8b 44 24 08 48 0b 85 48 00 00 00 74 28 48 8d 3d f1 63 1d 00 e8f
> 
> Code starting with the faulting instruction
> ===========================================
>     0:   8d a0 48 00 00 00       lea    0x48(%rax),%esp
>     6:   49 8b 44 24 08          mov    0x8(%r12),%rax
>     b:   48 0b 85 48 00 00 00    or     0x48(%rbp),%rax
>    12:   74 28                   je     0x3c
>    14:   48 8d 3d f1 63 1d 00    lea    0x1d63f1(%rip),%rdi        # 0x1d640c
>    1b:   8f                      .byte 0x8f
> [    7.442519] RSP: 002b:00007ffdfa53bc70 EFLAGS: 00010246
> [    7.443524] RAX: 0000000000000000 RBX: 00007f2ae19a7028 RCX: fffffffffffff000
> [    7.444857] RDX: 00007f2ae0f412e0 RSI: a3d70a3d70a3d70b RDI: 00007f2ae1656eb0
> [    7.446195] RBP: 00007f2ae0f40828 R08: 0000000000000001 R09: 00007f2ae19a7000
> [    7.447572] R10: 000055f8d50a1010 R11: 0000000000000246 R12: 00007f2ae0f40870
> [    7.448939] R13: 000055f8d50a7110 R14: 000055f8d50a2fd0 R15: 0000000000000001
> [    7.450277]  </TASK>
> [    7.450725] Modules linked in: ip_tables x_tables autofs4 raid10 raid456 libcrc32c async_raid6_recov 4
> [    7.454653] Dumping ftrace buffer:
> [    7.455321]    (ftrace buffer empty)
> [    7.456014] CR2: 0000000000000008
> [    7.456686] ---[ end trace 0000000000000000 ]---
> [    7.457576] RIP: 0010:_compound_head (include/linux/page-flags.h:245)
> [ 7.458440] Code: e8 35 b5 cd ff 5d c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 90f
> 
> Code starting with the faulting instruction
> ===========================================
>     0:   e8 35 b5 cd ff          callq  0xffffffffffcdb53a
>     5:   5d                      pop    %rbp
>     6:   c3                      retq
>     7:   cc                      int3
>     8:   cc                      int3
>     9:   cc                      int3
>     a:   cc                      int3
>     b:   66 66 2e 0f 1f 84 00    data16 nopw %cs:0x0(%rax,%rax,1)
>    12:   00 00 00 00
>    16:   0f 1f 40 00             nopl   0x0(%rax)
>    1a:   90                      nop
>    1b:   0f                      .byte 0xf
> [    7.461986] RSP: 0000:ffffb86140cd3d58 EFLAGS: 00010202
> [    7.463014] RAX: ffff96d3c19c4d38 RBX: ffffffffa103f080 RCX: 00000001019c4067
> [    7.464374] RDX: 0000000000000000 RSI: ffff96d2c0000d38 RDI: 0000000000000000
> [    7.465731] RBP: ffffb86140cd3d90 R08: ffff96d3c19c4d38 R09: 0000000000000067
> [    7.467114] R10: 0000000000000000 R11: 00007f2ae19d5fff R12: ffffb86140cd3dd0
> [    7.468469] R13: 0000000000000001 R14: ffff96d3cb7aa450 R15: 0000000000000860
> [    7.469824] FS:  00007f2ae0f40980(0000) GS:ffff96f1fd640000(0000) knlGS:0000000000000000
> [    7.471383] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    7.472482] CR2: 0000000000000008 CR3: 0000000104830000 CR4: 00000000000006e0
> [    7.473835] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    7.475216] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> Thanks,
> SJ
>