Default kern.ipc.shm_allow_removed to 1
John Baldwin
jhb at freebsd.org
Fri Aug 30 21:16:07 UTC 2013
On Friday, August 30, 2013 9:30:09 am George Liaskos wrote:
> Would it be feasible to change the default for 10?
>
> There is a lot of code that depends on the following behavior:
>
> void* address = shmat(shmkey, NULL /* desired address */, 0 /* flags */);
> // Here we mark the shared memory for deletion. Since we attached it in the
> // line above, it doesn't actually get deleted but, if we crash, this means
> // that the kernel will automatically clean it up for us.
> shmctl(shmkey, IPC_RMID, 0);
> if (address == kInvalidAddress)
> return NULL;
>
> The above snip is from Google Chrome, under FreeBSD with the current
> defaults that memory becomes unusable. If you don't follow that route
> it becomes extremely difficult to cleanup especially in a beast like
> Chrome.
>
> From what I understand PC-BSD defaults to 1, OpenBSD and Linux also
> allow this behavior.
>
> Am I missing something obvious here? It seems to me that the pragmatic
> approach is to change this.
Hmm, I can see why that is useful though it seems to violate POSIX. This
claims that IPC_RMID should delete the segment immediately (which does not
seem useful):
http://pubs.opengroup.org/onlinepubs/007904975/functions/shmctl.html
--
John Baldwin
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