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From: Jarkko Sakkinen <jarkko@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
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,
	Haitao Huang <haitao.huang@linux.intel.com>,
	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: Thu, 21 Jan 2021 02:26:56 +0200	[thread overview]
Message-ID: <YAjKUO+nI2pJs1HD@kernel.org> (raw)
In-Reply-To: <bb46fd98-0f67-76a7-9ba9-3a646c2a8f84@intel.com>

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

  reply	other threads:[~2021-01-21  2:09 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 [this message]
2021-01-22 18:20             ` Haitao Huang
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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