From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57455) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5WW2-0000xn-TA for qemu-devel@nongnu.org; Thu, 18 Jun 2015 05:53:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z5WVx-0007Gs-I3 for qemu-devel@nongnu.org; Thu, 18 Jun 2015 05:53:46 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:51104 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5WVx-0007Gh-29 for qemu-devel@nongnu.org; Thu, 18 Jun 2015 05:53:41 -0400 Message-ID: <55829515.6060701@kamp.de> Date: Thu, 18 Jun 2015 11:53:25 +0200 From: Peter Lieven MIME-Version: 1.0 References: <55803637.3060607@kamp.de> <20150617083539.GA4202@noname.str.redhat.com> <55826789.6080008@kamp.de> <55826C49.2030605@redhat.com> <55826D4B.3000703@kamp.de> <55826F41.70808@kamp.de> <20150618074500.GB4270@noname.redhat.com> <558281B2.6020905@kamp.de> <20150618084241.GC4270@noname.redhat.com> <55828F73.3080809@kamp.de> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-block] RFC cdrom in own thread? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , Paolo Bonzini , John Snow , qemu-devel , qemu block Am 18.06.2015 um 11:36 schrieb Stefan Hajnoczi: > On Thu, Jun 18, 2015 at 10:29 AM, Peter Lieven wrote: >> Am 18.06.2015 um 10:42 schrieb Kevin Wolf: >>> Am 18.06.2015 um 10:30 hat Peter Lieven geschrieben: >>>> Am 18.06.2015 um 09:45 schrieb Kevin Wolf: >>>>> Am 18.06.2015 um 09:12 hat Peter Lieven geschrieben: >>>>>> Thread 2 (Thread 0x7ffff5550700 (LWP 2636)): >>>>>> #0 0x00007ffff5d87aa3 in ppoll () from /lib/x86_64-linux-gnu/libc.so.6 >>>>>> No symbol table info available. >>>>>> #1 0x0000555555955d91 in qemu_poll_ns (fds=0x5555563889c0, nfds=3, >>>>>> timeout=4999424576) at qemu-timer.c:326 >>>>>> ts = {tv_sec = 4, tv_nsec = 999424576} >>>>>> tvsec = 4 >>>>>> #2 0x0000555555956feb in aio_poll (ctx=0x5555563528e0, blocking=true) >>>>>> at aio-posix.c:231 >>>>>> node = 0x0 >>>>>> was_dispatching = false >>>>>> ret = 1 >>>>>> progress = false >>>>>> #3 0x000055555594aeed in bdrv_prwv_co (bs=0x55555637eae0, >>>>>> offset=4292007936, >>>>>> qiov=0x7ffff554f760, is_write=false, flags=0) at block.c:2699 >>>>>> aio_context = 0x5555563528e0 >>>>>> co = 0x5555563888a0 >>>>>> rwco = {bs = 0x55555637eae0, offset = 4292007936, >>>>>> qiov = 0x7ffff554f760, is_write = false, ret = 2147483647, >>>>>> flags = 0} >>>>>> #4 0x000055555594afa9 in bdrv_rw_co (bs=0x55555637eae0, >>>>>> sector_num=8382828, >>>>>> buf=0x7ffff44cc800 "(", nb_sectors=4, is_write=false, flags=0) >>>>>> at block.c:2722 >>>>>> qiov = {iov = 0x7ffff554f780, niov = 1, nalloc = -1, size = >>>>>> 2048} >>>>>> iov = {iov_base = 0x7ffff44cc800, iov_len = 2048} >>>>>> #5 0x000055555594b008 in bdrv_read (bs=0x55555637eae0, >>>>>> sector_num=8382828, >>>>>> buf=0x7ffff44cc800 "(", nb_sectors=4) at block.c:2730 >>>>>> No locals. >>>>>> #6 0x000055555599acef in blk_read (blk=0x555556376820, >>>>>> sector_num=8382828, >>>>>> buf=0x7ffff44cc800 "(", nb_sectors=4) at block/block-backend.c:404 >>>>>> No locals. >>>>>> #7 0x0000555555833ed2 in cd_read_sector (s=0x555556408f88, >>>>>> lba=2095707, >>>>>> buf=0x7ffff44cc800 "(", sector_size=2048) at hw/ide/atapi.c:116 >>>>>> ret = 32767 >>>>> Here is the problem: The ATAPI emulation uses synchronous blk_read() >>>>> instead of the AIO or coroutine interfaces. This means that it keeps >>>>> polling for request completion while it holds the BQL until the request >>>>> is completed. >>>> I will look at this. >> >> I need some further help. My way to "emulate" a hung NFS Server is to >> block it in the Firewall. Currently I face the problem that I cannot mount >> a CD Iso via libnfs (nfs://) without hanging Qemu (i previously tried with >> a kernel NFS mount). It reads a few sectors and then stalls (maybe another >> bug): >> >> (gdb) thread apply all bt full >> >> Thread 3 (Thread 0x7ffff0c21700 (LWP 29710)): >> #0 qemu_cond_broadcast (cond=cond@entry=0x555556259940) at >> util/qemu-thread-posix.c:120 >> err = >> __func__ = "qemu_cond_broadcast" >> #1 0x0000555555911164 in rfifolock_unlock (r=r@entry=0x555556259910) at >> util/rfifolock.c:75 >> __PRETTY_FUNCTION__ = "rfifolock_unlock" >> #2 0x0000555555875921 in aio_context_release (ctx=ctx@entry=0x5555562598b0) >> at async.c:329 >> No locals. >> #3 0x000055555588434c in aio_poll (ctx=ctx@entry=0x5555562598b0, >> blocking=blocking@entry=true) at aio-posix.c:272 >> node = >> was_dispatching = false >> i = >> ret = >> progress = false >> timeout = 611734526 >> __PRETTY_FUNCTION__ = "aio_poll" >> #4 0x00005555558bc43d in bdrv_prwv_co (bs=bs@entry=0x55555627c0f0, >> offset=offset@entry=7038976, qiov=qiov@entry=0x7ffff0c208f0, >> is_write=is_write@entry=false, flags=flags@entry=(unknown: 0)) at >> block/io.c:552 >> aio_context = 0x5555562598b0 >> co = >> rwco = {bs = 0x55555627c0f0, offset = 7038976, qiov = >> 0x7ffff0c208f0, is_write = false, ret = 2147483647, flags = (unknown: 0)} >> #5 0x00005555558bc533 in bdrv_rw_co (bs=0x55555627c0f0, >> sector_num=sector_num@entry=13748, buf=buf@entry=0x555557874800 "(", >> nb_sectors=nb_sectors@entry=4, is_write=is_write@entry=false, >> flags=flags@entry=(unknown: 0)) at block/io.c:575 >> qiov = {iov = 0x7ffff0c208e0, niov = 1, nalloc = -1, size = 2048} >> iov = {iov_base = 0x555557874800, iov_len = 2048} >> #6 0x00005555558bc593 in bdrv_read (bs=, >> sector_num=sector_num@entry=13748, buf=buf@entry=0x555557874800 "(", >> nb_sectors=nb_sectors@entry=4) at block/io.c:583 >> No locals. >> #7 0x00005555558af75d in blk_read (blk=, >> sector_num=sector_num@entry=13748, buf=buf@entry=0x555557874800 "(", >> nb_sectors=nb_sectors@entry=4) at block/block-backend.c:493 >> ret = >> #8 0x00005555557abb88 in cd_read_sector (sector_size=, >> buf=0x555557874800 "(", lba=3437, s=0x55555760db70) at hw/ide/atapi.c:116 >> ret = >> #9 ide_atapi_cmd_reply_end (s=0x55555760db70) at hw/ide/atapi.c:190 >> byte_count_limit = >> size = >> ret = 2 > This is still the same scenario Kevin explained. > > The ATAPI CD-ROM emulation code is using synchronous blk_read(). This > function holds the QEMU global mutex while waiting for the I/O request > to complete. This blocks other vcpu threads and the main loop thread. > > The solution is to convert the CD-ROM emulation code to use > blk_aio_readv() instead of blk_read(). Yes, my problem was that I was using a libnfs version that was broken. I can now continue debugging. Sorry for the noise. A problem I faced is that 'info block' queries the allocated file size of the CDROM Image and thus hangs. I think nfs_get_allocated_file_size additionally needs a timeout? Peter