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SubjectRe: [PATCH] prctl.2: Document new PR_SET_CHILD_SUBREAPER semantics
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On 01/28/2017 01:47 AM, Michael Kerrisk (man-pages) wrote:
> Hello Pavel,
>
> On 27 January 2017 at 23:11, Pavel Tikhomirov <ptikhomirov@virtuozzo.com> wrote:
>> old semantics was non deterministic and worked differently
>> depending on the external factors, but nothing changes if
>> process first sets itself subreaper and only after forks
>
> When did the kernel behavior change?

Sorry for inconvenience, should have added you to cc of a main patch also.

Kernel behavior haven't changed yet, doc change will be a continuation
of "[PATCH v2 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic",
see https://lkml.org/lkml/2017/1/27/108

>
> Cheers,
>
> Michael
>
>
>> Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
>> ---
>> man2/prctl.2 | 24 +++++++++++++++++-------
>> 1 file changed, 17 insertions(+), 7 deletions(-)
>>
>> diff --git a/man2/prctl.2 b/man2/prctl.2
>> index 97cf21a..84fbd7e 100644
>> --- a/man2/prctl.2
>> +++ b/man2/prctl.2
>> @@ -162,20 +162,30 @@ if
>> is zero, unset the attribute.
>>
>> When a process is marked as a child subreaper,
>> -all of the children that it creates, and their descendants,
>> +all of the children that it creates or have created already, and their descendants,
>> will be marked as having a subreaper.
>> In effect, a subreaper fulfills the role of
>> .BR init (1)
>> for its descendant processes.
>> -Upon termination of a process
>> -that is orphaned (i.e., its immediate parent has already terminated)
>> -and marked as having a subreaper,
>> -the nearest still living ancestor subreaper
>> -will receive a
>> +Upon termination of a process having a subreaper,
>> +all its children become orphaned
>> +and will be reparented to the nearest still living ancestor subreaper.
>> +So that on it's adopted child termination
>> +these subreaper will receive a
>> .BR SIGCHLD
>> signal and will be able to
>> .BR wait (2)
>> -on the process to discover its termination status.
>> +on the child to discover its termination status.
>> +
>> +Note, that on older kernels these prctl works slightly different.
>> +Child subreaper process was not actualy the
>> +.BR init (1)
>> +for all its descendants.
>> +If process forks a child while not been a child subreaper,
>> +and after sets himself child subreaper,
>> +sub-tree of the child might or might not reparent to the subreaper,
>> +depending on the configuration of ancestors of the subreaper,
>> +at the time of forking our subtree.
>> .TP
>> .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"
>> Return the "child subreaper" setting of the caller,
>> --
>> 2.9.3
>>
>
>
>

--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.

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