linux-kernel - [PATCH for 4.18 3/3] rseq: cleanup: no need to abort rseq c.s. in child on fork

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Message-Id: <20180619133230.4087-4-mathieu.desnoyers@efficios.com>
Date:   Tue, 19 Jun 2018 09:32:30 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        linux-kselftest@...r.kernel.org
Subject: [PATCH for 4.18 3/3] rseq: cleanup: no need to abort rseq c.s. in child on fork

Considering that we explicitly forbid system calls in rseq critical
sections, it is not valid to issue a fork or clone system call within a
rseq critical section, so rseq_fork() is not required to restart an
active rseq c.s. in the child process.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Dave Watson <davejwatson@...com>
Cc: Will Deacon <will.deacon@....com>
Cc: Shuah Khan <shuahkh@....samsung.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: linux-kselftest@...r.kernel.org
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Chris Lameter <cl@...ux.com>
Cc: Russell King <linux@....linux.org.uk>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Paul Turner <pjt@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Maurer <bmaurer@...com>
Cc: linux-api@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
 include/linux/sched.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 87bf02d93a27..c1882643d455 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1831,9 +1831,7 @@ static inline void rseq_migrate(struct task_struct *t)
 
 /*
  * If parent process has a registered restartable sequences area, the
- * child inherits. Only applies when forking a process, not a thread. In
- * case a parent fork() in the middle of a restartable sequence, set the
- * resume notifier to force the child to retry.
+ * child inherits. Only applies when forking a process, not a thread.
  */
 static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags)
 {
@@ -1847,7 +1845,6 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags)
 		t->rseq_len = current->rseq_len;
 		t->rseq_sig = current->rseq_sig;
 		t->rseq_event_mask = current->rseq_event_mask;
-		rseq_preempt(t);
 	}
 }
 
-- 
2.11.0