From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49761) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5WFM-0007aG-9W for qemu-devel@nongnu.org; Thu, 18 Jun 2015 05:36:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z5WFL-0006i4-55 for qemu-devel@nongnu.org; Thu, 18 Jun 2015 05:36:32 -0400 MIME-Version: 1.0 In-Reply-To: <55828F73.3080809@kamp.de> 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> Date: Thu, 18 Jun 2015 10:36:29 +0100 Message-ID: From: Stefan Hajnoczi Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [Qemu-block] RFC cdrom in own thread? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: Kevin Wolf , Paolo Bonzini , John Snow , qemu-devel , qemu block 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(). Stefan