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Message-ID: <1869501326.16653.1510852171734.JavaMail.zimbra@efficios.com>
Date: Thu, 16 Nov 2017 17:09:31 +0000 (UTC)
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Boqun Feng <boqun.feng@...il.com>,
Andy Lutomirski <luto@...capital.net>,
Dave Watson <davejwatson@...com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-api <linux-api@...r.kernel.org>,
Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Russell King <linux@....linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
Ben Maurer <bmaurer@...com>, 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>,
Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH v11 for 4.15 01/24] Restartable sequences system
call
----- On Nov 16, 2017, at 11:32 AM, Peter Zijlstra peterz@...radead.org wrote:
> On Thu, Nov 16, 2017 at 04:27:07PM +0000, Mathieu Desnoyers wrote:
>> ----- On Nov 16, 2017, at 11:18 AM, Peter Zijlstra peterz@...radead.org wrote:
>>
>> > On Tue, Nov 14, 2017 at 03:03:51PM -0500, Mathieu Desnoyers wrote:
>> >> @@ -977,6 +978,13 @@ struct task_struct {
>> >> unsigned long numa_pages_migrated;
>> >> #endif /* CONFIG_NUMA_BALANCING */
>> >>
>> >> +#ifdef CONFIG_RSEQ
>> >> + struct rseq __user *rseq;
>> >> + u32 rseq_len;
>> >> + u32 rseq_sig;
>> >> + bool rseq_preempt, rseq_signal, rseq_migrate;
>> >
>> > No bool please. Use something that has a defined size in ILP32/LP64.
>> > _Bool makes it absolutely impossible to speculate on structure layout
>> > across architectures.
>>
>> I should as well make all those a bitmask within a "u32 rseq_event_mask" then,
>> sounds fair ?
>
> Sure, whatever works and isn't _Bool ;-)
So something along those lines should do the trick (including
the mask request from Ben Maurer):
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b995a3b..44aef30 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -982,7 +982,7 @@ struct task_struct {
struct rseq __user *rseq;
u32 rseq_len;
u32 rseq_sig;
- bool rseq_preempt, rseq_signal, rseq_migrate;
+ u32 rseq_event_mask;
#endif
struct tlbflush_unmap_batch tlb_ubc;
@@ -1676,6 +1676,16 @@ static inline void set_task_cpu(struct task_struct *p, un
#endif
#ifdef CONFIG_RSEQ
+/*
+ * Map the event mask on the user-space ABI enum rseq_cs_flags
+ * for direct mask checks.
+ */
+enum rseq_event_mask {
+ RSEQ_EVENT_PREEMPT = RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT,
+ RSEQ_EVENT_SIGNAL = RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL,
+ RSEQ_EVENT_MIGRATE = RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE,
+};
+
static inline void rseq_set_notify_resume(struct task_struct *t)
{
if (t->rseq)
@@ -1718,16 +1728,16 @@ static inline void rseq_sched_out(struct task_struct *t)
}
static inline void rseq_signal_deliver(struct pt_regs *regs)
{
- current->rseq_signal = true;
+ current->rseq_event_mask |= RSEQ_EVENT_SIGNAL;
rseq_handle_notify_resume(regs);
}
static inline void rseq_preempt(struct task_struct *t)
{
- t->rseq_preempt = true;
+ t->rseq_event_mask |= RSEQ_EVENT_PREEMPT;
}
static inline void rseq_migrate(struct task_struct *t)
{
- t->rseq_migrate = true;
+ t->rseq_event_mask |= RSEQ_EVENT_MIGRATE;
}
#else
static inline void rseq_set_notify_resume(struct task_struct *t)
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 6f0d48c..d773003 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -159,7 +159,7 @@ static bool rseq_get_rseq_cs(struct task_struct *t,
static int rseq_need_restart(struct task_struct *t, uint32_t cs_flags)
{
bool need_restart = false;
- uint32_t flags;
+ uint32_t flags, event_mask;
/* Get thread flags. */
if (__get_user(flags, &t->rseq->flags))
@@ -174,26 +174,17 @@ static int rseq_need_restart(struct task_struct *t, uint32
* a preempted signal handler could fail to restart the prior
* execution context on sigreturn.
*/
- if (flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL) {
- if (!(flags & RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE))
- return -EINVAL;
- if (!(flags & RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT))
+ if (unlikely(flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL)) {
+ if ((flags & (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
+ | RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT))
+ != (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
+ | RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT))
return -EINVAL;
}
- if (t->rseq_migrate
- && !(flags & RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE))
- need_restart = true;
- else if (t->rseq_preempt
- && !(flags & RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT))
- need_restart = true;
- else if (t->rseq_signal
- && !(flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL))
- need_restart = true;
-
- t->rseq_preempt = false;
- t->rseq_signal = false;
- t->rseq_migrate = false;
- if (need_restart)
+ event_mask = t->rseq_event_mask;
+ t->rseq_event_mask = 0;
+ event_mask &= ~flags;
+ if (event_mask)
return 1;
return 0;
}
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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