Re: [PATCH v1 3/3] util/oslib-posix: Support concurrent os_mem_prealloc() invocation

[David Hildenbrand <david@redhat.com>]

>>>
>>> Of course with the madvise impl we're bypassing the SIGBUS
>>> dance entirely. This is good for people with new kernels,
>>> but is this SIGBUS stuff safe for older kernels ?
>>
>> It remains broken with old kernels I guess. There isn't too much that we can
>> do: disabling prealloc=on once the VM is running breaks existing use cases.
> 
> Ok, while refactoring this, could you add a scary warning next to the
> sigaction calls mentioning that this code is not likely to play well
> with qemu's other handling of sigbus, as a reminder to future reviewers.

Sure thing!

> 
>> Fortunately, running into that race seems to be rare, at least I never hear
>> reports.
> 
> The failure mode is likely to be silent or easily mis-interpreted
> 
> Is there any value in emitting a one-time per process warning message
> on stderr if we take the old codepath post-startup ?

Will look into emitting a warning when running this code while the VM is 
already running. (hope it won't be too ugly to have vm state checks in 
util/oslib-posix).

-- 
Thanks,

David / dhildenb