Messages in this thread Patch in this message | | | From | Julia Cartwright <> | Subject | [PATCH RT 04/22] futex: Fix OWNER_DEAD fixup | Date | Mon, 6 Aug 2018 04:17:20 -0500 |
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From: Peter Zijlstra <peterz@infradead.org>
4.9.115-rt94-rc1 stable review patch. If you have any objection to the inclusion of this patch, let me know.
--- 8< --- 8< --- 8< --- [ Upstream commit a97cb0e7b3f4c6297fd857055ae8e895f402f501 ]
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: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Julia Cartwright <julia@ni.com> --- kernel/futex.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index cdd68ba6e3a6..57038131ad3f 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2301,9 +2301,6 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); oldowner = pi_state->owner; - /* Owner died? */ - if (!pi_state->owner) - newtid |= FUTEX_OWNER_DIED; /* * We are here because either: @@ -2364,6 +2361,9 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, } 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; -- 2.18.0
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