Re: futex question

From: Peter Zijlstra
Date: Mon Oct 05 2009 - 07:14:35 EST


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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