* qemu-img hangs on s390x
@ 2023-02-05 19:10 Michael Tokarev
2023-02-06 6:55 ` Philippe Mathieu-Daudé
0 siblings, 1 reply; 2+ messages in thread
From: Michael Tokarev @ 2023-02-05 19:10 UTC (permalink / raw)
To: QEMU Developers
There's a bug filed against qemu on debian, about qemu-img hanging on s390x.
While digging in, I discovered that the thing is broken there indeed, and it
is broken for a very long time, and it is interesting.
The reproducer is rather simple:
qemu-img create -f qcow2 -o preallocation=metadata blank-disk-1s.qcow2 512
this hangs until interrupted, after writing 327680 bytes of output.
I haven't tried old versions, - 5.2 hangs for sure, as is 7.2 and apparently
all in-between. In particular, current debian sid (whole thing) and 2-years
old debian bullseye hangs equally.
But the thing is that it does not hang when creating file on a tmpfs, -
when the filesystem is tmpfs, it always works.
Also, a few times I were able to run the above qemu-img create successfully, -
maybe 2 out of 100 runs or so.
It looks like the problem has been there for a very long time, and it is
timing-dependent.
Comparing strace of the two runs, I see differences in most futex operations.
Here's the parent process:
...
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
-futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 1
+futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
+futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 1
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
-futex(0x2aa29af8bb0, FUTEX_WAKE_PRIVATE, 1) = 1
+futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
-futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 1
+futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 0
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
-futex(0x2aa29af8bb0, FUTEX_WAKE_PRIVATE, 1) = 1
+futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
-futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 0
+futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 1
read(7, "\0\0\0\0\0\0\0\1", 512) = 8
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
-ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ? ERESTARTNOHAND (To be restarted if no handler)
ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
---- SIGINT {si_signo=SIGINT, si_code=SI_KERNEL} ---
-+++ killed by SIGINT +++
+futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
+read(7, "\0\0\0\0\0\0\0\1", 512) = 8
+ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1 ([{fd=7, revents=POLLIN}])
+futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 0
+read(7, "\0\0\0\0\0\0\0\1", 512) = 8
...
(I've hit Ctrl+C after quite some time).
I'll take another look at this tomorrow. But if someone knows
what's going on there, please tell me :) The situation is quite
interesting, - is it possible we missed such a serious issue somehow?
Thanks,
/mjt
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: qemu-img hangs on s390x
2023-02-05 19:10 qemu-img hangs on s390x Michael Tokarev
@ 2023-02-06 6:55 ` Philippe Mathieu-Daudé
0 siblings, 0 replies; 2+ messages in thread
From: Philippe Mathieu-Daudé @ 2023-02-06 6:55 UTC (permalink / raw)
To: Michael Tokarev, QEMU Developers
Cc: open list:S390 general arch..., Qemu-block
+s390x/block lists
On 5/2/23 20:10, Michael Tokarev wrote:
> There's a bug filed against qemu on debian, about qemu-img hanging on
> s390x.
> While digging in, I discovered that the thing is broken there indeed,
> and it
> is broken for a very long time, and it is interesting.
>
> The reproducer is rather simple:
>
> qemu-img create -f qcow2 -o preallocation=metadata blank-disk-1s.qcow2
> 512
>
> this hangs until interrupted, after writing 327680 bytes of output.
> I haven't tried old versions, - 5.2 hangs for sure, as is 7.2 and
> apparently
> all in-between. In particular, current debian sid (whole thing) and 2-years
> old debian bullseye hangs equally.
>
> But the thing is that it does not hang when creating file on a tmpfs, -
> when the filesystem is tmpfs, it always works.
>
> Also, a few times I were able to run the above qemu-img create
> successfully, -
> maybe 2 out of 100 runs or so.
>
> It looks like the problem has been there for a very long time, and it is
> timing-dependent.
>
> Comparing strace of the two runs, I see differences in most futex
> operations.
> Here's the parent process:
>
> ...
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> -futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 1
> +futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> +futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 1
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> -futex(0x2aa29af8bb0, FUTEX_WAKE_PRIVATE, 1) = 1
> +futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> -futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 1
> +futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 0
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> -futex(0x2aa29af8bb0, FUTEX_WAKE_PRIVATE, 1) = 1
> +futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> -futex(0x2aa29af8bb4, FUTEX_WAKE_PRIVATE, 1) = 0
> +futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 1
> read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> -ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = ?
> ERESTARTNOHAND (To be restarted if no handler)
> ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> ---- SIGINT {si_signo=SIGINT, si_code=SI_KERNEL} ---
> -+++ killed by SIGINT +++
> +futex(0x2aa03600bb4, FUTEX_WAKE_PRIVATE, 1) = 0
> +read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> +ppoll([{fd=7, events=POLLIN|POLLERR|POLLHUP}], 1, NULL, NULL, 8) = 1
> ([{fd=7, revents=POLLIN}])
> +futex(0x2aa03600bb0, FUTEX_WAKE_PRIVATE, 1) = 0
> +read(7, "\0\0\0\0\0\0\0\1", 512) = 8
> ...
>
> (I've hit Ctrl+C after quite some time).
>
> I'll take another look at this tomorrow. But if someone knows
> what's going on there, please tell me :) The situation is quite
> interesting, - is it possible we missed such a serious issue somehow?
>
> Thanks,
>
> /mjt
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-02-06 6:55 ` Philippe Mathieu-Daudé
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