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From: Florian Weimer <fweimer@redhat.com>
To: linux-api@vger.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Jann Horn <jannh@google.com>, libc-alpha@sourceware.org ,
	linux-kernel@vger.kernel.org
Subject: rseq + membarrier programming model
Date: Mon, 13 Dec 2021 19:47:57 +0100	[thread overview]
Message-ID: <87tufctk82.fsf@oldenburg.str.redhat.com> (raw)

I've been studying Jann Horn's biased locking example:

  Re: [PATCH 0/4 POC] Allow executing code and syscalls in another address space
  <https://lore.kernel.org/linux-api/CAG48ez02UDn_yeLuLF4c=kX0=h2Qq8Fdb0cer1yN8atbXSNjkQ@mail.gmail.com/>

It uses MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ as part of the biased lock
revocation.

How does the this code know that the process has called
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ?  Could it fall back to
MEMBARRIER_CMD_GLOBAL instead?  Why is it that MEMBARRIER_CMD_GLOBAL
does not require registration (the broader/more expensive barrier), but
the more restricted versions do?

Or put differently, why wouldn't we request
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ unconditionally at
process start in glibc, once we start biased locking in a few places?

Thanks,
Florian


             reply	other threads:[~2021-12-13 18:48 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-13 18:47 Florian Weimer [this message]
2021-12-13 19:19 ` Mathieu Desnoyers
2021-12-13 19:29   ` Florian Weimer
2021-12-13 19:56     ` Mathieu Desnoyers
2021-12-13 20:12       ` Florian Weimer
2021-12-14 20:25         ` Mathieu Desnoyers
2021-12-13 19:27 ` Jann Horn
2021-12-13 19:31 ` Mathieu Desnoyers

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