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From: "André Almeida" <andrealmeid@collabora.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Darren Hart <dvhart@infradead.org>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: kernel@collabora.com, krisman@collabora.com,
	pgriffais@valvesoftware.com, z.figura12@gmail.com,
	joel@joelfernandes.org, malteskarupke@fastmail.fm,
	linux-api@vger.kernel.org, fweimer@redhat.com,
	libc-alpha@sourceware.org, linux-kselftest@vger.kernel.org,
	shuah@kernel.org, acme@kernel.org, corbet@lwn.net,
	"Peter Oskolkov" <posk@posk.io>,
	"Andrey Semashev" <andrey.semashev@gmail.com>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@collabora.com>
Subject: [PATCH v4 15/15] kernel: Enable waitpid() for futex2
Date: Thu,  3 Jun 2021 16:59:24 -0300	[thread overview]
Message-ID: <20210603195924.361327-16-andrealmeid@collabora.com> (raw)
In-Reply-To: <20210603195924.361327-1-andrealmeid@collabora.com>

To make pthreads works as expected if they are using futex2, wake
clear_child_tid with futex2 as well. This is make applications that uses
waitpid() (and clone(CLONE_CHILD_SETTID)) wake while waiting for the
child to terminate. Given that apps should not mix futex() and futex2(),
any correct app will trigger a harmless noop wakeup on the interface
that it isn't using.

Signed-off-by: André Almeida <andrealmeid@collabora.com>
---

This commit is here for the intend to show what we need to do in order
to get a full NPTL working on top of futex2. It should be merged after
we talk to glibc folks on the details around the futex_wait() side. For
instance, we could use this as an opportunity to use private futexes or
8bit sized futexes, but both sides need to use the exactly same flags.
---
 include/linux/syscalls.h |  2 ++
 kernel/fork.c            |  2 ++
 kernel/futex2.c          | 30 ++++++++++++++++++------------
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index c108df6b3b82..94e0356ceeaa 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1324,6 +1324,8 @@ int ksys_ipc(unsigned int call, int first, unsigned long second,
 	unsigned long third, void __user * ptr, long fifth);
 int compat_ksys_ipc(u32 call, int first, int second,
 	u32 third, u32 ptr, u32 fifth);
+long ksys_futex_wake(void __user *uaddr, unsigned long nr_wake,
+		     unsigned int flags);
 
 /*
  * The following kernel syscall equivalents are just wrappers to fs-internal
diff --git a/kernel/fork.c b/kernel/fork.c
index dc06afd725cb..344430d882b1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1322,6 +1322,8 @@ static void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 			put_user(0, tsk->clear_child_tid);
 			do_futex(tsk->clear_child_tid, FUTEX_WAKE,
 					1, NULL, NULL, 0, 0);
+			ksys_futex_wake(tsk->clear_child_tid, 1,
+					FUTEX_32 | FUTEX_SHARED_FLAG);
 		}
 		tsk->clear_child_tid = NULL;
 	}
diff --git a/kernel/futex2.c b/kernel/futex2.c
index 5fd0b3d73b53..bf2de369b78a 100644
--- a/kernel/futex2.c
+++ b/kernel/futex2.c
@@ -978,18 +978,8 @@ static inline bool futex_match(struct futex_key key1, struct futex_key key2)
 		key1.offset == key2.offset);
 }
 
-/**
- * sys_futex_wake - Wake a number of futexes waiting on an address
- * @uaddr:   Address of futex to be woken up
- * @nr_wake: Number of futexes waiting in uaddr to be woken up
- * @flags:   Flags for size and shared
- *
- * Wake `nr_wake` threads waiting at uaddr.
- *
- * Returns the number of woken threads on success, error code otherwise.
- */
-SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
-		unsigned int, flags)
+long ksys_futex_wake(void __user *uaddr, unsigned long nr_wake,
+		     unsigned int flags)
 {
 	bool shared = (flags & FUTEX_SHARED_FLAG) ? true : false;
 	unsigned int size = flags & FUTEX_SIZE_MASK;
@@ -1023,6 +1013,22 @@ SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
 	return ret;
 }
 
+/**
+ * sys_futex_wake - Wake a number of futexes waiting on an address
+ * @uaddr:   Address of futex to be woken up
+ * @nr_wake: Number of futexes waiting in uaddr to be woken up
+ * @flags:   Flags for size and shared
+ *
+ * Wake `nr_wake` threads waiting at uaddr.
+ *
+ * Returns the number of woken threads on success, error code otherwise.
+ */
+SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
+		unsigned int, flags)
+{
+	return ksys_futex_wake(uaddr, nr_wake, flags);
+}
+
 static void futex_double_unlock(struct futex_bucket *b1, struct futex_bucket *b2)
 {
 	spin_unlock(&b1->lock);
-- 
2.31.1


  parent reply	other threads:[~2021-06-03 20:01 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-03 19:59 [PATCH v4 00/15] Add futex2 syscalls André Almeida
2021-06-03 19:59 ` [PATCH v4 01/15] futex2: Implement wait and wake functions André Almeida
2021-06-03 19:59 ` [PATCH v4 02/15] futex2: Add support for shared futexes André Almeida
2021-06-03 19:59 ` [PATCH v4 03/15] futex2: Implement vectorized wait André Almeida
2021-06-03 19:59 ` [PATCH v4 04/15] futex2: Implement requeue operation André Almeida
2021-06-03 19:59 ` [PATCH v4 05/15] futex2: Implement support for different futex sizes André Almeida
2021-06-04  0:23   ` kernel test robot
2021-06-06 19:12   ` Davidlohr Bueso
2021-06-06 23:01     ` Andrey Semashev
2021-06-03 19:59 ` [PATCH v4 06/15] futex2: Add compatibility entry point for x86_x32 ABI André Almeida
2021-06-03 19:59 ` [PATCH v4 07/15] docs: locking: futex2: Add documentation André Almeida
2021-06-06 19:23   ` Davidlohr Bueso
2021-06-03 19:59 ` [PATCH v4 08/15] selftests: futex2: Add wake/wait test André Almeida
2021-06-03 19:59 ` [PATCH v4 09/15] selftests: futex2: Add timeout test André Almeida
2021-06-03 19:59 ` [PATCH v4 10/15] selftests: futex2: Add wouldblock test André Almeida
2021-06-03 19:59 ` [PATCH v4 11/15] selftests: futex2: Add waitv test André Almeida
2021-06-03 19:59 ` [PATCH v4 12/15] selftests: futex2: Add requeue test André Almeida
2021-06-03 19:59 ` [PATCH v4 13/15] selftests: futex2: Add futex sizes test André Almeida
2021-06-03 19:59 ` [PATCH v4 14/15] perf bench: Add futex2 benchmark tests André Almeida
2021-06-03 19:59 ` André Almeida [this message]
2021-06-04  4:51 ` [PATCH v4 00/15] Add futex2 syscalls Zebediah Figura
2021-06-04 17:04   ` André Almeida
2021-06-04 11:36 ` Nicholas Piggin
2021-06-04 20:01   ` André Almeida
2021-06-05  1:09     ` Nicholas Piggin
2021-06-05  8:56       ` Andrey Semashev
2021-06-06 11:57         ` Nicholas Piggin
2021-06-06 13:15           ` Andrey Semashev
2021-06-08  1:25             ` Nicholas Piggin
2021-06-08 11:03               ` Andrey Semashev
2021-06-08 11:13                 ` Greg KH
2021-06-08 11:44                   ` Peter Zijlstra
2021-06-08 14:31                     ` Davidlohr Bueso
2021-06-08 12:06                   ` Andrey Semashev
2021-06-08 12:33                     ` Greg KH
2021-06-08 12:35                     ` Greg KH
2021-06-08 13:18                       ` Andrey Semashev
2021-06-08 13:27                         ` Greg KH
2021-06-08 13:41                           ` Andrey Semashev
2021-06-08 17:06                         ` Zebediah Figura
2021-06-08 14:14                   ` André Almeida
2021-06-07 15:40       ` André Almeida
2021-06-08  1:31         ` Nicholas Piggin
2021-06-08  2:33         ` Davidlohr Bueso
2021-06-08  4:45           ` Nicholas Piggin
2021-06-08 12:26         ` Sebastian Andrzej Siewior
2021-06-08 14:23           ` Peter Zijlstra
2021-06-08 14:57             ` Sebastian Andrzej Siewior
2021-06-08 15:04             ` André Almeida
2021-06-08 18:08             ` Adhemerval Zanella
2021-06-08 18:19               ` Florian Weimer
2021-06-08 18:22                 ` Adhemerval Zanella
2021-06-09 16:26             ` David Laight

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