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From: "Haitao Huang" <haitao.huang@linux.intel.com>
To: "Dave Hansen" <dave.hansen@intel.com>,
	"Jarkko Sakkinen" <jarkko@kernel.org>
Cc: "Borislav Petkov" <bp@alien8.de>,
	linux-sgx@vger.kernel.org, kai.huang@intel.com,
	haitao.huang@intel.com, seanjc@google.com,
	stable@vger.kernel.org, "Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Jethro Beekman" <jethro@fortanix.com>
Subject: Re: [PATCH v4] x86/sgx: Fix the call order of synchronize_srcu() in sgx_release()
Date: Fri, 22 Jan 2021 12:20:59 -0600	[thread overview]
Message-ID: <op.0xmvr1urwjvjmi@mqcpg7oapc828.gar.corp.intel.com> (raw)
In-Reply-To: <YAjKUO+nI2pJs1HD@kernel.org>

On Wed, 20 Jan 2021 18:26:56 -0600, Jarkko Sakkinen <jarkko@kernel.org>  
wrote:

> On Wed, Jan 20, 2021 at 09:34:10AM -0800, Dave Hansen wrote:
>> On 1/20/21 6:43 AM, Jarkko Sakkinen wrote:
>> >> So why do you need the synchronize_srcu() call when this process  
>> sees an
>> >> empty mm_list already?
>> >>
>> >> Thx.
>> > The other process aka some process using the enclave calls  
>> list_del_rcu()
>> > (and synchronize_srcu()), which starts a new grace period. If we don't
>> > do it, then the cleanup_srcu() will race with that grace period.
>>
>> To me, this is only a partial explanation.
>>
>> That goal of synchronize_srcu() is to wait for the completion of a
>> *previous* grace period: one that might have observed the old state of
>> the list.
>>
>> Could you explain the *actual* effects of the misplaced
>> synchronize_srcu()?  If the race _occurs_, what is the side-effect?
>
> As I haven't been able to reproduce this regression myself, I need
> to take steps back and try to reproduce the it with Graphene.
>
> WARN_ON()'s trigger inside cleanup_srcu_struct(), which causes a memory
> leak since free_percpu() gets never called. If I recall correctly, it
> was srcu_readers_active() but unfortunately I don't have a log available.
>
> Perhaps Haitao could provide us one.
>
> /Jarkko

Sorry I lost those logs too as our email server automatically clean up old  
emails. I have been re-running the tests but have not been able to  
reproduce the same issue.

Haitao

  reply	other threads:[~2021-01-22 18:39 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-15  1:46 [PATCH v4] x86/sgx: Fix the call order of synchronize_srcu() in sgx_release() jarkko
2021-01-15  7:18 ` Borislav Petkov
2021-01-16  5:12   ` Jarkko Sakkinen
2021-01-18 18:57     ` Borislav Petkov
2021-01-20 14:43       ` Jarkko Sakkinen
2021-01-20 17:34         ` Dave Hansen
2021-01-21  0:26           ` Jarkko Sakkinen
2021-01-22 18:20             ` Haitao Huang [this message]
2021-01-20 17:35 ` Sean Christopherson
2021-01-21  0:29   ` Jarkko Sakkinen
2021-01-21  1:19     ` Dave Hansen
2021-01-21 12:55       ` Jarkko Sakkinen
2021-01-21 18:19         ` Dave Hansen
2021-01-22 16:56   ` Dave Hansen
2021-01-23  8:58     ` Jarkko Sakkinen
2021-01-25 15:49       ` Dave Hansen
2021-01-27 17:31         ` Jarkko Sakkinen

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