From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>,
"Bulekov, Alexander" <alxndr@bu.edu>
Cc: "bsd@redhat.com" <bsd@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [PATCH v8 13/21] main: keep rcu_atfork callback enabled for qtest
Date: Thu, 30 Jan 2020 18:24:11 +0100 [thread overview]
Message-ID: <4bc49889-081e-6016-b8d5-a5d1fd615830@redhat.com> (raw)
In-Reply-To: <20200130144224.GC180311@stefanha-x1.localdomain>
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On 30/01/20 15:42, Stefan Hajnoczi wrote:
>> +
>> + /*
>> + * If QTest is enabled, keep the rcu_atfork enabled, since system processes
>> + * may be forked testing purposes (e.g. fork-server based fuzzing)
>> + */
>> + if (!qtest_enabled()) {
>> + rcu_disable_atfork();
>> + }
> I haven't reviewed the details of whether resources are leaked across
> fork but in general it makes sense that we want an RCU thread in the
> fork child:
Note that there is a possible deadlock between fork and synchronize_rcu
(see commit 73c6e40, "rcu: completely disable pthread_atfork callbacks
as soon as possible", 2016-01-27):
- the CPU thread is inside a RCU critical section and wants to take the
BQL in order to do MMIO
- the I/O thread, which is owning the BQL, forks and calls
rcu_init_lock, which tries to take the rcu_sync_lock
- the call_rcu thread has taken rcu_sync_lock in synchronize_rcu, but
synchronize_rcu needs the CPU thread to end the critical section before
returning.
Therefore it would be best if the fork server could fork before a single
CPU instruction is executed, and then rcu_disable_atfork could be moved
right after the fork server is started (just like right now we do it
right after os_daemonize). We probably talked about this before, but
how do you ensure that the fork server is started before threads are
created (apart from the RCU thread)?
Paolo
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next prev parent reply other threads:[~2020-01-30 17:25 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 5:34 [PATCH v8 00/21] Add virtual device fuzzing support Bulekov, Alexander
2020-01-29 5:34 ` [PATCH v8 01/21] softmmu: split off vl.c:main() into main.c Bulekov, Alexander
2020-01-30 14:39 ` Stefan Hajnoczi
2020-01-30 15:06 ` Alex Bennée
2020-01-30 17:44 ` Alexander Bulekov
2020-01-30 18:41 ` Alex Bennée
2020-02-05 14:02 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 02/21] module: check module wasn't already initialized Bulekov, Alexander
2020-01-29 5:34 ` [PATCH v8 03/21] fuzz: add FUZZ_TARGET module type Bulekov, Alexander
2020-02-05 11:28 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 04/21] qtest: add qtest_server_send abstraction Bulekov, Alexander
2020-02-05 11:30 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 05/21] libqtest: add a layer of abstraction to send/recv Bulekov, Alexander
2020-02-05 11:32 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 06/21] libqtest: make bufwrite rely on the TransportOps Bulekov, Alexander
2020-02-05 11:36 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 07/21] qtest: add in-process incoming command handler Bulekov, Alexander
2020-02-05 11:39 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 08/21] libqos: rename i2c_send and i2c_recv Bulekov, Alexander
2020-02-05 11:40 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 09/21] libqos: split qos-test and libqos makefile vars Bulekov, Alexander
2020-01-29 5:34 ` [PATCH v8 10/21] libqos: move useful qos-test funcs to qos_external Bulekov, Alexander
2020-01-29 10:03 ` Paolo Bonzini
2020-02-05 13:34 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 11/21] fuzz: add fuzzer skeleton Bulekov, Alexander
2020-02-05 11:55 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 12/21] exec: keep ram block across fork when using qtest Bulekov, Alexander
2020-02-05 13:00 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 13/21] main: keep rcu_atfork callback enabled for qtest Bulekov, Alexander
2020-01-30 14:42 ` Stefan Hajnoczi
2020-01-30 17:24 ` Paolo Bonzini [this message]
2020-01-30 17:42 ` Alexander Bulekov
2020-01-30 18:14 ` Paolo Bonzini
2020-02-05 13:58 ` Darren Kenny
2020-06-18 7:34 ` Thomas Huth
2020-06-18 15:08 ` Alexander Bulekov
2020-01-29 5:34 ` [PATCH v8 14/21] fuzz: support for fork-based fuzzing Bulekov, Alexander
2020-01-29 5:34 ` [PATCH v8 16/21] fuzz: add target/fuzz makefile rules Bulekov, Alexander
2020-01-29 5:34 ` [PATCH v8 15/21] fuzz: add support for qos-assisted fuzz targets Bulekov, Alexander
2020-02-05 13:18 ` Darren Kenny
2020-02-11 16:19 ` Alexander Bulekov
2020-01-29 5:34 ` [PATCH v8 17/21] fuzz: add configure flag --enable-fuzzing Bulekov, Alexander
2020-02-05 13:19 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 18/21] fuzz: add i440fx fuzz targets Bulekov, Alexander
2020-02-05 13:26 ` Darren Kenny
2020-02-06 14:47 ` Alexander Bulekov
2020-01-29 5:34 ` [PATCH v8 19/21] fuzz: add virtio-net fuzz target Bulekov, Alexander
2020-01-30 14:43 ` Stefan Hajnoczi
2020-02-05 13:57 ` Darren Kenny
2020-02-06 14:51 ` Alexander Bulekov
2020-01-29 5:34 ` [PATCH v8 20/21] fuzz: add virtio-scsi " Bulekov, Alexander
2020-02-05 13:31 ` Darren Kenny
2020-01-29 5:34 ` [PATCH v8 21/21] fuzz: add documentation to docs/devel/ Bulekov, Alexander
2020-02-05 13:33 ` Darren Kenny
2020-01-30 14:44 ` [PATCH v8 00/21] Add virtual device fuzzing support Stefan Hajnoczi
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