From: Oleg Nesterov <oleg@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
Anton Blanchard <anton@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/3] kernel/uprobes: Fix check for active uprobe
Date: Fri, 29 Sep 2017 18:54:25 +0200 [thread overview]
Message-ID: <20170929165425.GA21087@redhat.com> (raw)
In-Reply-To: <20170929132723.GA2318@linux.vnet.ibm.com>
On 09/29, Srikar Dronamraju wrote:
>
> > This is correct because we do this check under mmap_sem so we can't race with
> > install_breakpoint(), so is_trap_at_addr() == T can't be falsely true if
> > UPROBE_COPY_INSN is not set.
> >
>
> Right, Given that we are doing this in the mmap_sem, we should also be
> removing the rmb/wmb pairs too.
Well, down_read(&mm->mmap_sem) can only guarantee that this mm can not be
modified by install_breakpoint().
But what if, say, another task with different ->mm does uprobe_mmap() and
calls prepare_uprobe() for the 1st time?
Or suppose we race with unregister+register...
OTOH, I agree that we can remove these barriers, but this needs a lengthy
comment while the current code looks "obviously correct" in that you do
not even need to think about potential races.
Oleg.
prev parent reply other threads:[~2017-09-29 16:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-22 9:13 [PATCH v3 0/3] A few uprobe fixes Naveen N. Rao
2017-09-22 9:13 ` [PATCH v3 1/3] kernel/uprobes: Do away with uprobe_warn() Naveen N. Rao
2017-09-22 9:13 ` [PATCH v3 2/3] kernel/uprobes: Warn if unable to install breakpoint Naveen N. Rao
2017-09-22 9:13 ` [PATCH v3 3/3] kernel/uprobes: Fix check for active uprobe Naveen N. Rao
2017-09-25 16:16 ` Oleg Nesterov
2017-09-28 7:06 ` Ingo Molnar
2017-09-29 13:27 ` Srikar Dronamraju
2017-09-29 16:54 ` Oleg Nesterov [this message]
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