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Tue, 16 Jul 2024 22:03:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHVT6zbwClVl+Iqr5cWcyx85w3o+8Wvh1FDT0tZOUXOTkXjRfqRL1TjpWo29ss80g4efIHDyA== X-Received: by 2002:a05:600c:4e92:b0:426:6388:d59f with SMTP id 5b1f17b1804b1-427c2cadf1emr3306345e9.1.1721192617770; Tue, 16 Jul 2024 22:03:37 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Sergey Dyasli Subject: [PULL 02/20] Revert "qemu-char: do not operate on sources from finalize callbacks" Date: Wed, 17 Jul 2024 07:03:12 +0200 Message-ID: <20240717050331.295371-3-pbonzini@redhat.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240717050331.295371-1-pbonzini@redhat.com> References: <20240717050331.295371-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1721192858439116600 Content-Type: text/plain; charset="utf-8" From: Sergey Dyasli This reverts commit 2b316774f60291f57ca9ecb6a9f0712c532cae34. After 038b4217884c ("Revert "chardev: use a child source for qio input source"") we've been observing the "iwp->src =3D=3D NULL" assertion triggering periodically during the initial capabilities querying by libvirtd. One of possible backtraces: Thread 1 (Thread 0x7f16cd4f0700 (LWP 43858)): 0 __GI_raise (sig=3Dsig@entry=3D6) at ../sysdeps/unix/sysv/linux/raise.c:50 1 0x00007f16c6c21e65 in __GI_abort () at abort.c:79 2 0x00007f16c6c21d39 in __assert_fail_base at assert.c:92 3 0x00007f16c6c46e86 in __GI___assert_fail (assertion=3Dassertion@entry=3D= 0x562e9bcdaadd "iwp->src =3D=3D NULL", file=3Dfile@entry=3D0x562e9bcdaac8 "= ../chardev/char-io.c", line=3Dline@entry=3D99, function=3Dfunction@entry=3D= 0x562e9bcdab10 <__PRETTY_FUNCTION__.20549> "io_watch_poll_finalize") at ass= ert.c:101 4 0x0000562e9ba20c2c in io_watch_poll_finalize (source=3D) = at ../chardev/char-io.c:99 5 io_watch_poll_finalize (source=3D) at ../chardev/char-io.= c:88 6 0x00007f16c904aae0 in g_source_unref_internal () from /lib64/libglib-2.0= .so.0 7 0x00007f16c904baf9 in g_source_destroy_internal () from /lib64/libglib-2= .0.so.0 8 0x0000562e9ba20db0 in io_remove_watch_poll (source=3D0x562e9d6720b0) at = ../chardev/char-io.c:147 9 remove_fd_in_watch (chr=3Dchr@entry=3D0x562e9d5f3800) at ../chardev/char= -io.c:153 10 0x0000562e9ba23ffb in update_ioc_handlers (s=3D0x562e9d5f3800) at ../cha= rdev/char-socket.c:592 11 0x0000562e9ba2072f in qemu_chr_fe_set_handlers_full at ../chardev/char-f= e.c:279 12 0x0000562e9ba207a9 in qemu_chr_fe_set_handlers at ../chardev/char-fe.c:3= 04 13 0x0000562e9ba2ca75 in monitor_qmp_setup_handlers_bh (opaque=3D0x562e9d4c= 2c60) at ../monitor/qmp.c:509 14 0x0000562e9bb6222e in aio_bh_poll (ctx=3Dctx@entry=3D0x562e9d4c2f20) at = ../util/async.c:216 15 0x0000562e9bb4de0a in aio_poll (ctx=3D0x562e9d4c2f20, blocking=3Dblockin= g@entry=3Dtrue) at ../util/aio-posix.c:722 16 0x0000562e9b99dfaa in iothread_run (opaque=3D0x562e9d4c26f0) at ../iothr= ead.c:63 17 0x0000562e9bb505a4 in qemu_thread_start (args=3D0x562e9d4c7ea0) at ../ut= il/qemu-thread-posix.c:543 18 0x00007f16c70081ca in start_thread (arg=3D) at pthread_cr= eate.c:479 19 0x00007f16c6c398d3 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clon= e.S:95 io_remove_watch_poll(), which makes sure that iwp->src is NULL, calls g_source_destroy() which finds that iwp->src is not NULL in the finalize callback. This can only happen if another thread has managed to trigger io_watch_poll_prepare() callback in the meantime. Move iwp->src destruction back to the finalize callback to prevent the described race, and also remove the stale comment. The deadlock glib bug was fixed back in 2010 by b35820285668 ("gmain: move finalization of GSource outside of context lock"). Suggested-by: Paolo Bonzini Signed-off-by: Sergey Dyasli Link: https://lore.kernel.org/r/20240712092659.216206-1-sergey.dyasli@nutan= ix.com Signed-off-by: Paolo Bonzini --- chardev/char-io.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) diff --git a/chardev/char-io.c b/chardev/char-io.c index dab77b112e3..3be17b51ca5 100644 --- a/chardev/char-io.c +++ b/chardev/char-io.c @@ -87,16 +87,12 @@ static gboolean io_watch_poll_dispatch(GSource *source,= GSourceFunc callback, =20 static void io_watch_poll_finalize(GSource *source) { - /* - * Due to a glib bug, removing the last reference to a source - * inside a finalize callback causes recursive locking (and a - * deadlock). This is not a problem inside other callbacks, - * including dispatch callbacks, so we call io_remove_watch_poll - * to remove this source. At this point, iwp->src must - * be NULL, or we would leak it. - */ IOWatchPoll *iwp =3D io_watch_poll_from_source(source); - assert(iwp->src =3D=3D NULL); + if (iwp->src) { + g_source_destroy(iwp->src); + g_source_unref(iwp->src); + iwp->src =3D NULL; + } } =20 static GSourceFuncs io_watch_poll_funcs =3D { @@ -139,11 +135,6 @@ static void io_remove_watch_poll(GSource *source) IOWatchPoll *iwp; =20 iwp =3D io_watch_poll_from_source(source); - if (iwp->src) { - g_source_destroy(iwp->src); - g_source_unref(iwp->src); - iwp->src =3D NULL; - } g_source_destroy(&iwp->parent); } =20 --=20 2.45.2