Re: [Qemu-devel] [question] mask SIGBUS in qemu main thread

[Alex Bennée]

gengdongjiu <gengdong...@huawei.com> writes:

> Hi all,
>   sorry to disturb you, I have a question to consult with you why the SIGBUS 
> mask bit is set in the Qemu main thread?
> do we not want to Qemu main thread to handle the SIGBUS signal?
>   thanks.

What exactly do you expect the main thread to do with a SIGBUS signal?

If QEMU doesn't catch the SIGBUS it will be up to the kernel to deal
with it, probably by terminating QEMU. This is fine because this is a
bug in QEMU that shouldn't have occurred.

This is different from dealing with SIGBUS due to the guests action
which might occur in the various vCPU threads.

> As shown in [1], the Qemu main thread PID is 30976.
> "cat /proc/30976/status" in [2], we can see the "SigBlk: 0000000010002240", 
> SIGBUS block bit is 7, so the SIGBUS block bit is set.
> then the Qemu main thread will not be woken up if there is SIGBUS set to it.
> thanks!
>
>
> [1]:
> # ps -eL | grep "qemu"
> 30976 30976 pts/7    00:00:00 qemu-system-x86
> 30976 30977 pts/7    00:00:00 qemu-system-x86
>
> [2]
> # cat /proc/30976/status
> Name:   qemu-system-x86
> State:  S (sleeping)
> Tgid:   30976
> Ngid:   0
> Pid:    30976
> PPid:   34807
> TracerPid:      0
> Uid:    1000    1000    1000    1000
> Gid:    1000    1000    1000    1000
> FDSize: 256
> Groups: 4 24 27 30 46 108 114 115 1000
> NStgid: 30976
> NSpid:  30976
> NSpgid: 30976
> NSsid:  34772
> VmPeak:   604260 kB
> VmSize:   538724 kB
> VmLck:         0 kB
> VmPin:         0 kB
> VmHWM:     34176 kB
> VmRSS:     34176 kB
> VmData:   294308 kB
> VmStk:       136 kB
> VmExe:      4808 kB
> VmLib:     36144 kB
> VmPTE:       528 kB
> VmPMD:        16 kB
> VmSwap:        0 kB
> HugetlbPages:          0 kB
> Threads:        2
> SigQ:   6/514067
> SigPnd: 0000000000000000
> ShdPnd: 0000000000000000
> SigBlk: 0000000010002240
> SigIgn: 0000000000001000
> SigCgt: 0000000180004243
> CapInh: 0000000000000000
> CapPrm: 0000000000000000
> CapEff: 0000000000000000
> CapBnd: 0000003fffffffff
> CapAmb: 0000000000000000
> Seccomp:        0
> Cpus_allowed:   ffff,ffffffff
> Cpus_allowed_list:      0-47
> Mems_allowed:   00000000,00000003
> Mems_allowed_list:      0-1
> voluntary_ctxt_switches:        7638
> nonvoluntary_ctxt_switches:     3


--
Alex Bennée