linux-kernel - Re: futex question

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Date:	Mon, 05 Oct 2009 13:16:12 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Anirban Sinha <ani@...rban.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Darren Hart <dvhltc@...ibm.com>,
	Kaz Kylheku <kaz@...gmasystems.com>,
	Anirban Sinha <asinha@...gmasystems.com>
Subject: Re: futex question

On Mon, 2009-10-05 at 12:56 +0200, Thomas Gleixner wrote:
> 
> Looking more into that I think we should check whether the robust list
> has an entry (lock held) in do_execve() and return -EWOULDBLOCK to
> luser space. Same if pi_waiters is not empty. Holding a lock and
> calling execve() is simply broken.

Fine by me ;-)

something like the below?

The question is of course what Ani was doing that triggered this in the
first place and if he can live with this.. :-)

---
 fs/exec.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d49be6b..0812ba6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1295,6 +1295,22 @@ int do_execve(char * filename,
 	bool clear_in_exec;
 	int retval;
 
+	retval = -EWOULDBLOCK;
+#ifdef CONFIG_FUTEX
+	if (unlikely(current->robust_list))
+		goto out_ret;
+#ifdef CONFIG_COMPAT
+	if (unlikely(current->compat_robust_list))
+		goto out_ret;
+#endif
+	spin_lock_irq(&current->pi_lock);
+	if (!list_empty(&current->pi_state_list)) {
+		spin_unlock_irq(&current->pi_lock);
+		goto out_ret;
+	}
+	spin_unlock_irq(&current->pi_lock);
+#endif
+
 	retval = unshare_files(&displaced);
 	if (retval)
 		goto out_ret;


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