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From: Peter Lieven <pl@kamp.de>
Message-ID: <577B620A.5010202@kamp.de>
Date: Tue, 5 Jul 2016 09:30:18 +0200
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Subject: Re: [Qemu-devel] Regression: block: Add .bdrv_co_pwrite_zeroes()
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To: Eric Blake <eblake@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Kevin Wolf <kwolf@redhat.com>

Am 05.07.2016 um 03:53 schrieb Eric Blake:
> On 07/04/2016 07:49 AM, Peter Lieven wrote:
>> Hi,
>>
>> the above commit:
>>
>> commit d05aa8bb4a8b6aa9a915ec5074fb12ae632d2323
>> Author: Eric Blake <eblake@redhat.com>
>> Date:   Wed Jun 1 15:10:03 2016 -0600
>>
>>      block: Add .bdrv_co_pwrite_zeroes()
>>
>> introduces a regression (at least for me).
>>
>> The Limits from the iSCSI Block Limits VPD have no requirement of being
>> a power of two.
>> We use Dell Equallogic iSCSI SANs for instance. They have an internal
>> page size of 15MB. And
>> they advertise this page size as max_ws_len, opt_transfer_len and
>> opt_discard_alignment.
> A non-power-of-2 max_ws_len shouldn't be a problem, but opt_transfer_len
> and opt_discard_alignment not being a power of 2 impacts other code.
> 15MB is a rather odd page size.

I know, not my idea ;-) I think at least opt_discard_alignment of 15MB used to work
before.

>
>> I think we cannot assert that that these alignments are a power of 2.
> Perhaps that means we should just fix our code to round things down to
> the nearest power of 2 (8MB) for the opt_transfer_len and
> opt_discard_alignment values.  Can you post a stack-trace of the actual
> assertion you are hitting?
>

Sure:

qemu-system-x86_64: block/io.c:1165: bdrv_co_do_pwrite_zeroes: Assertion `is_power_of_2(alignment)' failed.

Program received signal SIGABRT, Aborted.
0x00007ffff5222c37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56    ../nptl/sysdeps/unix/sysv/linux/raise.c: Datei oder Verzeichnis nicht gefunden.
(gdb) bt full
#0  0x00007ffff5222c37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
         resultvar = 0
         pid = 9610
         selftid = 9610
#1  0x00007ffff5226028 in __GI_abort () at abort.c:89
         save_stage = 2
         act = {__sigaction_handler = {sa_handler = 0x7fffffffe1fe, sa_sigaction = 0x7fffffffe1fe}, sa_mask = {__val = {140737307379972,
               93824998987040, 1165, 93823560581120, 140737306023251, 0, 93825220359792, 47244640260, 93825009612448, 256, 0, 0, 0, 21474836480,
               140737354027008, 140737307395000}}, sa_flags = 1438406118, sa_restorer = 0x555555bc5ca0 <__PRETTY_FUNCTION__.34924>}
         sigs = {__val = {32, 0 <repeats 15 times>}}
#2  0x00007ffff521bbf6 in __assert_fail_base (fmt=0x7ffff536c3b8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n",
     assertion=assertion@entry=0x555555bc55e6 "is_power_of_2(alignment)", file=file@entry=0x555555bc5520 "block/io.c", line=line@entry=1165,
     function=function@entry=0x555555bc5ca0 <__PRETTY_FUNCTION__.34924> "bdrv_co_do_pwrite_zeroes") at assert.c:92
         str = 0x5555586f5780 ""
         total = 4096
#3  0x00007ffff521bca2 in __GI___assert_fail (assertion=assertion@entry=0x555555bc55e6 "is_power_of_2(alignment)",
     file=file@entry=0x555555bc5520 "block/io.c", line=line@entry=1165,
     function=function@entry=0x555555bc5ca0 <__PRETTY_FUNCTION__.34924> "bdrv_co_do_pwrite_zeroes") at assert.c:101
No locals.
#4  0x0000555555a8a968 in bdrv_co_do_pwrite_zeroes (bs=bs@entry=0x5555565b2df0, offset=offset@entry=1359998976, count=count@entry=4096,
     flags=flags@entry=6) at block/io.c:1165
         drv = 0x5555560b3580 <bdrv_raw>
         qiov = {iov = 0x100000000, niov = 4096, nalloc = 0, size = 140737148473344}
         iov = {iov_base = 0x0, iov_len = 0}
         ret = 0
         need_flush = false
         head = 0
         tail = 0
         max_write_zeroes = <optimized out>
         alignment = 15728640
         __PRETTY_FUNCTION__ = "bdrv_co_do_pwrite_zeroes"
#5  0x0000555555a8ae3b in bdrv_aligned_pwritev (bs=bs@entry=0x5555565b2df0, req=req@entry=0x555562ee3970, offset=offset@entry=1359998976,
     bytes=bytes@entry=4096, qiov=0x555558909e58, flags=<optimized out>, flags@entry=0) at block/io.c:1290
---Type <return> to continue, or q <return> to quit---
         drv = 0x5555560b3580 <bdrv_raw>
         waited = <optimized out>
         ret = <optimized out>
         start_sector = 2656248
         end_sector = 2656256
         __PRETTY_FUNCTION__ = "bdrv_aligned_pwritev"
#6  0x0000555555a8b95f in bdrv_co_pwritev (bs=0x5555565b2df0, offset=offset@entry=1359998976, bytes=bytes@entry=4096,
     qiov=qiov@entry=0x555558909e58, flags=flags@entry=0) at block/io.c:1514
         req = {bs = 0x5555565b2df0, offset = 1359998976, bytes = 4096, type = BDRV_TRACKED_WRITE, serialising = false,
           overlap_offset = 1359998976, overlap_bytes = 4096, list = {le_next = 0x55555a3c9cc0, le_prev = 0x5555565b5f28}, co = 0x555557ccc100,
           wait_queue = {entries = {tqh_first = 0x0, tqh_last = 0x555562ee39b8}}, waiting_for = 0x0}
         align = 512
         head_buf = 0x0
         tail_buf = <optimized out>
         local_qiov = {iov = 0x0, niov = 1448841360, nalloc = 21845, size = 0}
         use_local_qiov = <optimized out>
         ret = <optimized out>
         __PRETTY_FUNCTION__ = "bdrv_co_pwritev"
#7  0x0000555555a7cae3 in blk_co_pwritev (blk=0x5555565b2c30, offset=1359998976, bytes=4096, qiov=0x555558909e58, flags=0)
     at block/block-backend.c:788
         ret = <optimized out>
#8  0x0000555555a7cc2e in blk_aio_write_entry (opaque=0x555557da5200) at block/block-backend.c:977
         acb = 0x555557da5200
         rwco = 0x555557da5228
#9  0x0000555555afafda in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at util/coroutine-ucontext.c:78
         self = 0x555557ccc100
         co = 0x555557ccc100
#10 0x00007ffff5235800 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
No symbol table info available.
#11 0x00007fffffffcf20 in ?? ()
No symbol table info available.
#12 0x0000000000000000 in ?? ()
No symbol table info available.

Peter