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Message-ID: <cf4acbb6-2815-56e2-829c-4e4c3a549e21@gmail.com>
Date: Thu, 30 Aug 2018 14:26:51 +0800
From: Jia He <hejianet@...il.com>
To: Jia He <hejianet@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: broonie@...nel.org, mhocko@...e.cz, sfr@...b.auug.org.au,
linux-next@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
mm-commits@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: mmotm 2018-08-23-17-26 uploaded
Hi Andrew
On 8/30/2018 9:00 AM, Jia He Wrote:
>
>
> On 8/30/2018 7:22 AM, Andrew Morton Wrote:
>> On Tue, 28 Aug 2018 12:20:46 +0800 Jia He <hejianet@...il.com> wrote:
>>
>>> Hi Andrew
>>> FYI,I watched a lockdep warning based on your mmotm master branch[1]
>>
>> Thanks. We'll need help from ARM peeps on this please.
>>
>>> [ 6.692731] ------------[ cut here ]------------
>>> [ 6.696391] DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled)
>>> [ 6.696404] WARNING: CPU: 3 PID: 320 at kernel/locking/lockdep.c:3845
>>> check_flags.part.38+0x9c/0x16c
>>> [ 6.711082] Modules linked in:
>>> [ 6.714101] CPU: 3 PID: 320 Comm: modprobe Not tainted 4.18.0-rc4-mm1+ #56
>>> [ 6.720956] Hardware name: WIWYNN HXT REP-1 System H001-00001-0/HXT REP-1
>>> CRB, BIOS 0ACJA530 03/20/2018
>>> [ 6.730332] pstate: 60400085 (nZCv daIf +PAN -UAO)
>>> [ 6.735106] pc : check_flags.part.38+0x9c/0x16c
>>> [ 6.739619] lr : check_flags.part.38+0x9c/0x16c
>>> [ 6.744133] sp : ffff80178536fbf0
>>> [ 6.747432] x29: ffff80178536fbf0 x28: ffff8017905a1b00
>>> [ 6.752727] x27: 0000000000000002 x26: 0000000000000000
>>> [ 6.758022] x25: ffff000008abeb14 x24: 0000000000000000
>>> [ 6.763317] x23: 0000000000000001 x22: 0000000000000001
>>> [ 6.768612] x21: 0000000000000001 x20: 0000000000000000
>>> [ 6.773908] x19: ffff00000a041000 x18: 0000000000000000
>>> [ 6.779202] x17: 0000000000000000 x16: 0000000000000000
>>> [ 6.784498] x15: 0000000000000000 x14: 0000000000000000
>>> [ 6.789793] x13: ffff000008d6b190 x12: 752ce9eb60de3f00
>>> [ 6.795088] x11: ffff80178536f7f0 x10: ffff80178536f7f0
>>> [ 6.800383] x9 : 00000000ffffffd0 x8 : 0000000000000000
>>> [ 6.805678] x7 : ffff00000816fe48 x6 : ffff801794ba62b8
>>> [ 6.810973] x5 : 0000000000000000 x4 : 0000000000000000
>>> [ 6.816269] x3 : ffffffffffffffff x2 : ffff0000091ed988
>>> [ 6.821564] x1 : 752ce9eb60de3f00 x0 : 752ce9eb60de3f00
>>> [ 6.826859] Call trace:
>>> [ 6.829290] check_flags.part.38+0x9c/0x16c
>>> [ 6.833457] lock_acquire+0x12c/0x280
>>> [ 6.837104] down_read_trylock+0x78/0x98
>>> [ 6.841011] do_page_fault+0x150/0x480
>>> [ 6.844742] do_translation_fault+0x74/0x80
>>> [ 6.848909] do_mem_abort+0x60/0x108
>>> [ 6.852467] el0_da+0x24/0x28
>>> [ 6.855418] irq event stamp: 250
>>> [ 6.858633] hardirqs last enabled at (249): [<ffff00000830e518>]
>>> mem_cgroup_commit_charge+0x9c/0x13c
>>> [ 6.867833] hardirqs last disabled at (250): [<ffff000008095f40>]
>>> el0_svc_handler+0xc4/0x16c
>>> [ 6.876252] softirqs last enabled at (242): [<ffff000008081c48>]
>>> __do_softirq+0x2f8/0x554
>>> [ 6.884501] softirqs last disabled at (229): [<ffff0000080f1bec>]
>>> irq_exit+0x180/0x194
>>> [ 6.892399] ---[ end trace b45768f94a7b7d9f ]---
>>> [ 6.896998] possible reason: unannotated irqs-on.
>>> [ 6.901685] irq event stamp: 250
>>> [ 6.904898] hardirqs last enabled at (249): [<ffff00000830e518>]
>>> mem_cgroup_commit_charge+0x9c/0x13c
>>> [ 6.914100] hardirqs last disabled at (250): [<ffff000008095f40>]
>>> el0_svc_handler+0xc4/0x16c
>>> [ 6.922519] softirqs last enabled at (242): [<ffff000008081c48>]
>>> __do_softirq+0x2f8/0x554
>>> [ 6.930766] softirqs last disabled at (229): [<ffff0000080f1bec>]
>>> irq_exit+0x180/0x194
>>> [ 7.023827] Initialise system trusted keyrings
>>> [ 7.027414] workingset: timestamp_bits=45 max_order=25 bucket_order=0
>>
>> Lockdep says current->hardirqs_enabled is false and that is indeed an
>> error. arch/arm64/kernel/entry.S:el0_da does enable_daif which might
>> be an attempt to enable hardirqs, but how does that get propagated into
>> lockdep's ->hardirqs_enabled? By calling
>> local_irq_enable()->trace_hardirqs_on(), but that's C, not assembler.
>>
>> And what changed to cause this?
>>
>> I dunno anything. Help!
>>
>>> I thought the root cause might be at [2] which seems not in your branch yet.
>>>
>>> [1] http://git.cmpxchg.org/cgit.cgi/linux-mmotm.git
>>> [2]
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=efd112
>>
>> I agree, that doesn't look like the culprit. But something may well
>> have gone wrong in "the recent conversion of the syscall entry/exit
>> code to C".
> Sorry for my unclearly previously description.
> 1. no such lockdep warning in latest mainline kernel git tree.
> 2. there is a 100% producible warning based on your latest mmotm tree
> 3. after applying the commit efd112 based on your mmotm tree, the warning
> disappearred
>
> I will do some further digging to answer your question if no other experts' help
>
1. in el0_svc->el0_svc_common, without commit efd112
local_daif_mask(); //disable the irq and trace irq off
flags = current_thread_info()->flags;
if (!has_syscall_work(flags))
------------ //1
return;
If el0_svc_common enters the logic at line 1, the irq is disabled and
current->hardirqs_enabled is 0.
2. then it goes to el0_da
in el0_da, it enables the irq without changing current->hardirqs_enabled to 1
3. goes to el0_da->do_mem_abort->... the lockdep warning happens
The commit efd112 fixes it by invoking trace_hardirqs_off at line 1.
It closes the inconsistency window.
Cheers,
Jia
--
Cheers,
Jia
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