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[1/1] futex: Fix OWNER_DEAD fixup

Message ID 20210222040618.2911498-2-zhengyejian1@huawei.com
State New
Headers show
Series Bugfix for ad4740ceccfb ("futex: Avoid violating the 10th rule of futex") | expand

Commit Message

Zheng Yejian Feb. 22, 2021, 4:06 a.m. UTC 
From: Peter Zijlstra <peterz@infradead.org>

commit a97cb0e7b3f4c6297fd857055ae8e895f402f501 upstream.

Both Geert and DaveJ reported that the recent futex commit:

  c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")

introduced a problem with setting OWNER_DEAD. We set the bit on an
uninitialized variable and then entirely optimize it away as a
dead-store.

Move the setting of the bit to where it is more useful.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Link: http://lkml.kernel.org/r/20180122103947.GD2228@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
 kernel/futex.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Comments

Zheng Yejian Feb. 22, 2021, 11:22 a.m. UTC | #1 
On 2021/2/22 18:16, Greg KH wrote:
> On Mon, Feb 22, 2021 at 12:06:18PM +0800, Zheng Yejian wrote:
>> From: Peter Zijlstra <peterz@infradead.org>
>>
>> commit a97cb0e7b3f4c6297fd857055ae8e895f402f501 upstream.
> 
> Why is this not also needed in 4.9.y?  If so, please also provide a
> backport there so I can apply this one too.
> 

I've sent a backport for 4.9.y, please review it.
Thanks~
diff mbox series

Patch

diff --git a/kernel/futex.c b/kernel/futex.c
index 199e63c5b612..70ad21bbb1d5 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2248,10 +2248,6 @@  static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
 
 	oldowner = pi_state->owner;
 
-	/* Owner died? */
-	if (!pi_state->owner)
-		newtid |= FUTEX_OWNER_DIED;
-
 	/*
 	 * We are here because either:
 	 *
@@ -2309,6 +2305,9 @@  retry:
 	}
 
 	newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+	/* Owner died? */
+	if (!pi_state->owner)
+		newtid |= FUTEX_OWNER_DIED;
 
 	if (get_futex_value_locked(&uval, uaddr))
 		goto handle_fault;