Re: [PATCH v2] Document /proc/pid PID reuse behavior

Vlastimil Babka
2018-11-20T09:05:27Z

On 11/19/18 11:54 AM, Pavel Machek wrote:
> On Mon 2018-11-05 13:22:05, Daniel Colascione wrote:
>> State explicitly that holding a /proc/pid file descriptor open does
>> not reserve the PID. Also note that in the event of PID reuse, these
>> open file descriptors refer to the old, now-dead process, and not the
>> new one that happens to be named the same numeric PID.
>>
>> Signed-off-by: Daniel Colascione <dancol@google.com>
>> ---
>> Documentation/filesystems/proc.txt | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> Moved paragraphed to start of /proc/pid section; added signed-off-by.
>>
>> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
>> index 12a5e6e693b6..0b14460f721d 100644
>> --- a/Documentation/filesystems/proc.txt
>> +++ b/Documentation/filesystems/proc.txt
>> @@ -125,6 +125,13 @@ process running on the system, which is named after the process ID (PID).
>> The link self points to the process reading the file system. Each process
>> subdirectory has the entries listed in Table 1-1.
>>
>> +Note that an open a file descriptor to /proc/<pid> or to any of its
>> +contained files or subdirectories does not prevent <pid> being reused
>> +for some other process in the event that <pid> exits. Operations on
>
> "does not" -> "may not"?
>
> We want to leave this unspecified, so that we can change it in future.

Why can't the documentation describe the current implementation, and
change in the future if the implementation changes? I doubt somebody
would ever rely on the pid being reused while having the descriptor
open. How would that make sense?
Pavel
>
>