linux-kernel - RE: futex question

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Date:	Thu, 1 Oct 2009 16:46:16 -0700
From:	"Anirban Sinha" <ASinha@...gmasystems.com>
To:	"Ingo Molnar" <mingo@...e.hu>, "Darren Hart" <dvhltc@...ibm.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: futex question


> Should we not just clear the pointer (and
>> it's compat version) within do_execve()?


In our private repository, applying the following patch resolved the
issues I mentioned. I no longer see messages like this:

 [futex] ("ifconfig")(pid=2509) exit_robust_list:unable to fetch robust
entry. uaddr=0x000000002abbc4f0

from my instrumented kernel within exit_robust_list(). My
instrumentation looked something like this:

if (fetch_robust_entry(...)) {
printk(...);
return;
}

Just tossing the patch in the community in case someone is interested
...



Signed-off-by: Anirban Sinha <asinha@...gmasystems.com>
---
 fs/compat.c |    3 +++
 fs/exec.c   |    3 +++
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/fs/compat.c b/fs/compat.c
index 6d6f98f..c3d117c 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1510,6 +1510,9 @@ int compat_do_execve(char * filename,
        if (retval)
                goto out_file;

+#ifdef CONFIG_FUTEX
+       current->compat_robust_list = NULL;
+#endif
        bprm->argc = compat_count(argv, MAX_ARG_STRINGS);
        if ((retval = bprm->argc) < 0)
                goto out;
diff --git a/fs/exec.c b/fs/exec.c
index 172ceb6..e9334b8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1323,6 +1323,9 @@ int do_execve(char * filename,
        retval = bprm_mm_init(bprm);
        if (retval)
                goto out_file;
+#ifdef CONFIG_FUTEX
+       current->robust_list = NULL;
+#endif

        bprm->argc = count(argv, MAX_ARG_STRINGS);
        if ((retval = bprm->argc) < 0)


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