From: Dave Hansen <dave.hansen@intel.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Sean Christopherson <seanjc@google.com>,
linux-sgx@vger.kernel.org, kai.huang@intel.com,
haitao.huang@intel.com, stable@vger.kernel.org,
Haitao Huang <haitao.huang@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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: Mon, 25 Jan 2021 07:49:04 -0800 [thread overview]
Message-ID: <5b881022-d9f1-3ac4-89e5-7da6d6ce2fc8@intel.com> (raw)
In-Reply-To: <YAvlLxCfN88Ii5qb@kernel.org>
Haitao managed to create another splat over the weekend. It was, indeed:
> WARNING: CPU: 3 PID: 7620 at kernel/rcu/srcutree.c:374 cleanup_srcu_struct+0xed/0x100
which is:
> if (WARN_ON(!srcu_get_delay(ssp)))
> return; /* Just leak it! */
That check means that there is an outstanding "expedited" grace period.
The fact that it's expedited is not important. This:
https://lwn.net/Articles/202847/
describes the reasoning behind the warning:
If the struct srcu_struct is dynamically allocated, then
cleanup_srcu_struct() must be called before it is freed ... the
caller must take care to ensure that all SRCU read-side critical
sections have completed (and that no more will commence) before
calling cleanup_srcu_struct().
synchronize_srcu() will (obviously) wait for the grace period to
complete. Calling it will shut up the warning for sure, most of the time.
The required sequence of events is in here:
> https://lore.kernel.org/lkml/1492472726-3841-4-git-send-email-paulmck@linux.vnet.ibm.com/
I suspect that the mmu notifier's synchronize_srcu() is run in parallel
very close to when cleanup_srcu_struct() is called. This violates the
"prevent any further calls to synchronize_srcu" rule.
So, while I suspect that adding a synchronize_srcu() is *part* of the
correct solution, I'm still not convinced that the
sgx_mmu_notifier_release() code is correct.
next prev parent reply other threads:[~2021-01-25 15:50 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
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 [this message]
2021-01-27 17:31 ` Jarkko Sakkinen
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