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McKenney" , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Alexander Viro Message-ID: <777590253.2016.1522245960189.JavaMail.zimbra@efficios.com> In-Reply-To: <20180328064703.56hsuicmikejg7np@tardis> References: <20180327160542.28457-1-mathieu.desnoyers@efficios.com> <20180327160542.28457-3-mathieu.desnoyers@efficios.com> <20180328064703.56hsuicmikejg7np@tardis> Subject: Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.7_GA_1964 (ZimbraWebClient - FF52 (Linux)/8.8.7_GA_1964) Thread-Topic: rseq: Introduce restartable sequences system call (v12) Thread-Index: giprJFg0sw1tC1sJYpw5uUx6Rdd1NA== Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: ----- On Mar 28, 2018, at 2:47 AM, Boqun Feng boqun.feng@gmail.com wrote: > On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote: > [...] >> Changes since v11: >> >> - Replace task struct rseq_preempt, rseq_signal, and rseq_migrate >> bool by u32 rseq_event_mask. > [...] >> @@ -979,6 +980,17 @@ 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; >> + /* >> + * RmW on rseq_event_mask must be performed atomically >> + * with respect to preemption. >> + */ >> + unsigned long rseq_event_mask; > > s/unsigned long/u32 good point, fixed. > >> +#endif >> + >> struct tlbflush_unmap_batch tlb_ubc; >> >> struct rcu_head rcu; >> @@ -1688,4 +1700,110 @@ extern long sched_getaffinity(pid_t pid, struct cpumask >> *mask); >> #define TASK_SIZE_OF(tsk) TASK_SIZE >> #endif >> > > [...] > >> + >> +static int rseq_ip_fixup(struct pt_regs *regs) >> +{ >> + unsigned long ip = instruction_pointer(regs), start_ip = 0, >> + post_commit_offset = 0, abort_ip = 0; >> + struct task_struct *t = current; >> + uint32_t cs_flags = 0; >> + bool in_rseq_cs = false; > > This seems unnecessary? Because.. > >> + int ret; >> + >> + ret = rseq_get_rseq_cs(t, &start_ip, &post_commit_offset, &abort_ip, >> + &cs_flags); >> + if (ret) >> + return ret; >> + >> + /* >> + * Handle potentially not being within a critical section. >> + * Unsigned comparison will be true when >> + * ip >= start_ip, and when ip < start_ip + post_commit_offset. >> + */ >> + if (ip - start_ip < post_commit_offset) >> + in_rseq_cs = true; >> + >> + /* >> + * If not nested over a rseq critical section, restart is >> + * useless. Clear the rseq_cs pointer and return. >> + */ >> + if (!in_rseq_cs) >> + return clear_rseq_cs(t); > > we can write > > if (ip - start_ip >= post_commit_offset) > return clear_rseq_cs(t); Good point. In a previous version, rseq_get_rseq_cs() had to conditionally update in_rseq_cs, but it's not the case anymore, so your approach indeed cleans up the code. Thanks! Mathieu > > Regards, > Boqun > >> + ret = rseq_need_restart(t, cs_flags); >> + if (ret <= 0) >> + return ret; >> + ret = clear_rseq_cs(t); >> + if (ret) >> + return ret; >> + trace_rseq_ip_fixup(ip, start_ip, post_commit_offset, abort_ip); >> + instruction_pointer_set(regs, (unsigned long)abort_ip); >> + return 0; >> +} >> + > [...] -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com