Re: Several tst-robust* tests time out with recent Linux kernel

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Tue, Nov 14, 2023 at 05:43:20PM +0100, Florian Weimer wrote:
> * Peter Zijlstra:
> 
> >> diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
> >> index b5379c0e6d6d..1a1f9301251f 100644
> >> --- a/kernel/futex/futex.h
> >> +++ b/kernel/futex/futex.h
> >> @@ -17,7 +17,7 @@
> >>   * restarts.
> >>   */
> >>  #ifdef CONFIG_MMU
> >> -# define FLAGS_SHARED		0x01
> >> +# define FLAGS_SHARED		0x10
> >>  #else
> >>  /*
> >>   * NOMMU does not have per process address space. Let the compiler optimize
> >
> > Just the above seems sufficient.
> 
> There are a few futex_wake calls which hard-code the flags argument as
> 1:
> 
> kernel/futex/core.c=637=static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
> --
> kernel/futex/core.c-686-         * this.
> kernel/futex/core.c-687-         */
> kernel/futex/core.c-688-        owner = uval & FUTEX_TID_MASK;
> kernel/futex/core.c-689-
> kernel/futex/core.c-690-        if (pending_op && !pi && !owner) {
> kernel/futex/core.c:691:                futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
> kernel/futex/core.c-692-                return 0;
> kernel/futex/core.c-693-        }
> kernel/futex/core.c-694-
> kernel/futex/core.c-695-        if (owner != task_pid_vnr(curr))
> kernel/futex/core.c-696-                return 0;
> --
> kernel/futex/core.c-739-        /*
> kernel/futex/core.c-740-         * Wake robust non-PI futexes here. The wakeup of
> kernel/futex/core.c-741-         * PI futexes happens in exit_pi_state():
> kernel/futex/core.c-742-         */
> kernel/futex/core.c-743-        if (!pi && (uval & FUTEX_WAITERS))
> kernel/futex/core.c:744:                futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
> kernel/futex/core.c-745-
> kernel/futex/core.c-746-        return 0;
> kernel/futex/core.c-747-}
> kernel/futex/core.c-748-
> kernel/futex/core.c-749-/*

Urgh, thanks!

Confirmed, the below cures things. Although I should probably make that
FLAGS_SIZE_32 | FLAGS_SHARED against Linus' tree.

Let me go do a proper patch.

---
 kernel/futex/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index d1d7b3c175a4..e7793f0d5757 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -687,7 +687,7 @@ static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
 	owner = uval & FUTEX_TID_MASK;
 
 	if (pending_op && !pi && !owner) {
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+		futex_wake(uaddr, FLAGS_SHARED, 1, FUTEX_BITSET_MATCH_ANY);
 		return 0;
 	}
 
@@ -740,7 +740,7 @@ static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
 	 * PI futexes happens in exit_pi_state():
 	 */
 	if (!pi && (uval & FUTEX_WAITERS))
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+		futex_wake(uaddr, FLAGS_SHARED, 1, FUTEX_BITSET_MATCH_ANY);
 
 	return 0;
 }