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([2a04:ee41:4:31cb:e591:1e1e:abde:a8f1]) by smtp.gmail.com with ESMTPSA id hr17sm2933083ejc.57.2021.12.17.08.38.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 08:38:33 -0800 (PST) Message-ID: <9ca5c434-ddf6-2ed3-08ae-92da5fc98013@redhat.com> Date: Fri, 17 Dec 2021 17:38:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v5 28/31] block.c: assert BQL lock held in bdrv_co_invalidate_cache To: Hanna Reitz , qemu-block@nongnu.org References: <20211124064418.3120601-1-eesposit@redhat.com> <20211124064418.3120601-29-eesposit@redhat.com> <56deaef1-6a4e-c544-9916-42a20cc20c7a@redhat.com> From: Emanuele Giuseppe Esposito In-Reply-To: <56deaef1-6a4e-c544-9916-42a20cc20c7a@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eesposit@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=eesposit@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -51 X-Spam_score: -5.2 X-Spam_bar: ----- X-Spam_report: (-5.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.718, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.716, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Cc: Kevin Wolf , Fam Zheng , Vladimir Sementsov-Ogievskiy , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , Juan Quintela , qemu-devel@nongnu.org, John Snow , Richard Henderson , Markus Armbruster , "Dr. David Alan Gilbert" , Stefan Hajnoczi , Paolo Bonzini , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 17/12/2021 12:04, Hanna Reitz wrote: > On 24.11.21 07:44, Emanuele Giuseppe Esposito wrote: >> bdrv_co_invalidate_cache is special: it is an I/O function, > > I still don’t believe it is, but well. > > (Yes, it is called by a test in an iothread, but I believe we’ve seen > that the tests simply sometimes test things that shouldn’t be allowed.) > >> but uses the block layer permission API, which is GS. >> >> Because of this, we can assert that either the function is >> being called with BQL held, and thus can use the permission API, >> or make sure that the permission API is not used, by ensuring that >> bs (and parents) .open_flags does not contain BDRV_O_INACTIVE. >> >> Signed-off-by: Emanuele Giuseppe Esposito >> --- >>   block.c | 26 ++++++++++++++++++++++++++ >>   1 file changed, 26 insertions(+) >> >> diff --git a/block.c b/block.c >> index a0309f827d..805974676b 100644 >> --- a/block.c >> +++ b/block.c >> @@ -6574,6 +6574,26 @@ void bdrv_init_with_whitelist(void) >>       bdrv_init(); >>   } >> +static bool bdrv_is_active(BlockDriverState *bs) >> +{ >> +    BdrvChild *parent; >> + >> +    if (bs->open_flags & BDRV_O_INACTIVE) { >> +        return false; >> +    } >> + >> +    QLIST_FOREACH(parent, &bs->parents, next_parent) { >> +        if (parent->klass->parent_is_bds) { >> +            BlockDriverState *parent_bs = parent->opaque; > > This looks like a really bad hack to me.  We purposefully have made the > parent link opaque so that a BDS cannot easily reach its parents.  All > accesses should go through BdrvChildClass methods. > > I also don’t understand why we need to query parents at all.  The only > fact that determines whether the current BDS will have its permissions > changed is whether the BDS itself is active or inactive.  Sure, we’ll > invoke bdrv_co_invalidate_cache() on the parents, too, but then we could > simply let the assertion fail there. > >> +            if (!bdrv_is_active(parent_bs)) { >> +                return false; >> +            } >> +        } >> +    } >> + >> +   return true; >> +} >> + >>   int coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs, >> Error **errp) >>   { >>       BdrvChild *child, *parent; >> @@ -6585,6 +6605,12 @@ int coroutine_fn >> bdrv_co_invalidate_cache(BlockDriverState *bs, Error **errp) >>           return -ENOMEDIUM; >>       } >> +    /* >> +     * No need to muck with permissions if bs is active. >> +     * TODO: should activation be a separate function? >> +     */ >> +    assert(qemu_in_main_thread() || bdrv_is_active(bs)); >> + > > I don’t understand this, really.  It looks to me like “if you don’t call > this in the main thread, this better be a no-op”, i.e., you must never > call this function in an I/O thread if you really want to use it.  I.e. > what I’d classify as a GS function. > > It sounds like this is just a special case for said test, and > special-casing code for tests sounds like a bad idea. Ok, but trying to leave just the qemu_in_main_thread() assertion makes test 307 (./check 307) fail. I am actually not sure on why it fails, but I am sure it is because of the assertion, since without it it passes. I tried with gdb (./check -gdb 307 on one terminal and gdb -iex "target remote localhost:12345" in another) but it points me to this below, which I think is the ndb server getting the socket closed (because on the other side it crashed), and not the actual error. Thread 1 "qemu-system-x86" received signal SIGPIPE, Broken pipe. 0x00007ffff68af54d in sendmsg () from target:/lib64/libc.so.6 (gdb) bt #0 0x00007ffff68af54d in sendmsg () from target:/lib64/libc.so.6 #1 0x0000555555c13cc9 in qio_channel_socket_writev (ioc=, iov=0x5555569a4870, niov=1, fds=0x0, nfds=, errp=0x0) at ../io/channel-socket.c:561 #2 0x0000555555c19b18 in qio_channel_writev_full_all (ioc=0x55555763b800, iov=iov@entry=0x7fffe8dffd80, niov=niov@entry=1, fds=fds@entry=0x0, nfds=nfds@entry=0, errp=errp@entry=0x0) at ../io/channel.c:240 #3 0x0000555555c19bd2 in qio_channel_writev_all (errp=0x0, niov=1, iov=0x7fffe8dffd80, ioc=) at ../io/channel.c:220 #4 qio_channel_write_all (ioc=, buf=buf@entry=0x7fffe8dffdd0 "", buflen=buflen@entry=20, errp=errp@entry=0x0) at ../io/channel.c:330 #5 0x0000555555c27e75 in nbd_write (errp=0x0, size=20, buffer=0x7fffe8dffdd0, ioc=) at ../nbd/nbd-internal.h:71 #6 nbd_negotiate_send_rep_len (client=client@entry=0x555556f60930, type=type@entry=1, len=len@entry=0, errp=errp@entry=0x0) at ../nbd/server.c:203 #7 0x0000555555c29db1 in nbd_negotiate_send_rep (errp=0x0, type=1, client=0x555556f60930) at ../nbd/server.c:211 --Type for more, q to quit, c to continue without paging-- #8 nbd_negotiate_options (errp=0x7fffe8dffe88, client=) at ../nbd/server.c:1224 #9 nbd_negotiate (errp=0x7fffe8dffe88, client=) at ../nbd/server.c:1340 #10 nbd_co_client_start (opaque=) at ../nbd/server.c:2715 #11 0x0000555555d70423 in coroutine_trampoline (i0=, i1=) at ../util/coroutine-ucontext.c:173 #12 0x00007ffff67f3820 in ?? () from target:/lib64/libc.so.6 #13 0x00007fffffffca80 in ?? () Emanuele > > Hanna > >>       QLIST_FOREACH(child, &bs->children, next) { >>           bdrv_co_invalidate_cache(child->bs, &local_err); >>           if (local_err) { >