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From: Florian Weimer <fw@deneb.enyo.de>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH] Remove cached PID/TID in clone
References: <1476387924-4509-1-git-send-email-adhemerval.zanella@linaro.org>
	<c432ff40-edf2-1ebe-f3a7-de76fbfdd252@redhat.com>
	<d0b874df-d9f7-6121-6786-6ac1292a82ec@linaro.org>
Date: Tue, 08 Nov 2016 20:11:00 -0000
In-Reply-To: <d0b874df-d9f7-6121-6786-6ac1292a82ec@linaro.org> (Adhemerval
	Zanella's message of "Tue, 8 Nov 2016 17:58:38 -0200")
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* Adhemerval Zanella:

>> It's a hotspot for incorrect/broken fork detection.
>
> If you mean the assert on fork.c, I review the code and it seems
> unnecessary to remove the assert on child creation:

No, something else entirely.  OpenSSL mixes the current PID into the
randomness pool, in an attempt to make sure that the streams generated
by parent and child are different:

    pid_t curr_pid =3D getpid();
=E2=80=A6
        if (curr_pid) {         /* just in the first iteration to save time=
 */
            if (!MD_Update(m, (unsigned char *)&curr_pid, sizeof curr_pid))
                goto err;
            curr_pid =3D 0;
        }

<https://github.com/openssl/openssl/blob/master/crypto/rand/md_rand.c#L283>

This happens at every invocation of RAND_bytes.  It may show up in
profiles if all the other system calls (time, gettimeofday etc.) are
handled by the vDSO.

But I suggest that this shouldn't block your change.  It's just
something we should be aware of.  If the kernel provides a more
efficient way to get the PID, we can change glibc to use it.

More comments about your revised patch tomorrow.