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Violators will be prosecuted; Tue, 6 Feb 2018 14:15:49 -0500 Received: from b01ledav006.gho.pok.ibm.com (b01ledav006.gho.pok.ibm.com [9.57.199.111]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w16JFnGC40960148; Tue, 6 Feb 2018 19:15:49 GMT Received: from b01ledav006.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D9027AC041; Tue, 6 Feb 2018 14:17:09 -0500 (EST) Received: from localhost (unknown [9.80.97.150]) by b01ledav006.gho.pok.ibm.com (Postfix) with ESMTP id 98880AC03F; Tue, 6 Feb 2018 14:17:09 -0500 (EST) From: Michael Roth To: qemu-devel@nongnu.org Date: Tue, 6 Feb 2018 13:14:47 -0600 X-Mailer: git-send-email 2.11.0 In-Reply-To: <20180206191515.25830-1-mdroth@linux.vnet.ibm.com> References: <20180206191515.25830-1-mdroth@linux.vnet.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 18020619-0036-0000-0000-000002BA0AC7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008485; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000248; SDB=6.00985885; UDB=6.00500282; IPR=6.00765253; BA=6.00005813; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00019407; XFM=3.00000015; UTC=2018-02-06 19:15:51 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18020619-0037-0000-0000-0000433F814A Message-Id: <20180206191515.25830-27-mdroth@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2018-02-06_09:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1802060241 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by mx0b-001b2d01.pphosted.com id w16JEJcV056297 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.158.5 Subject: [Qemu-devel] [PATCH 26/54] linux-user: Fix locking order in fork_start() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , qemu-stable@nongnu.org, christian.ehrhardt@canonical.com, Laurent Vivier Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Type: text/plain; charset="utf-8" From: Peter Maydell Our locking order is that the tb lock should be taken inside the mmap_lock, but fork_start() grabs locks the other way around. This means that if a heavily multithreaded guest process (such as Java) calls fork() it can deadlock, with the thread that called fork() stuck in fork_start() with the tb lock and waiting for the mmap lock, but some other thread in tb_find() with the mmap lock and waiting for the tb lock. The cpu_list_lock() should also always be taken last, not first. Fix this by making fork_start() grab the locks in the right order. The order in which we drop locks doesn't matter, so we leave fork_end() the way it is. Signed-off-by: Peter Maydell Cc: qemu-stable@nongnu.org Reviewed-by: Paolo Bonzini Reviewed-by: Alex Benn=C3=A9e Message-Id: <1512397331-15238-1-git-send-email-peter.maydell@linaro.org> Signed-off-by: Laurent Vivier (cherry picked from commit 024949caf32805f4cc3e7d363a80084b47aac1f6) Signed-off-by: Michael Roth --- linux-user/main.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/linux-user/main.c b/linux-user/main.c index 6286661bd3..146ee3e4ba 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -128,9 +128,9 @@ int cpu_get_pic_interrupt(CPUX86State *env) /* Make sure everything is in a consistent state for calling fork(). */ void fork_start(void) { - cpu_list_lock(); - qemu_mutex_lock(&tb_ctx.tb_lock); mmap_fork_start(); + qemu_mutex_lock(&tb_ctx.tb_lock); + cpu_list_lock(); } =20 void fork_end(int child) --=20 2.11.0