From: Peter Zijlstra <peterz@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: KVM list <kvm@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
pmladek@suse.cz, Andy Lutomirski <luto@amacapital.net>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
xen-devel <Xen-devel@lists.xen.org>,
Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup_exception
Date: Mon, 4 Apr 2016 14:46:34 +0200 [thread overview]
Message-ID: <20160404124634.GS3430__5398.43225055865$1459774079$gmane$org@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160404115206.GG8372@quack.suse.cz>
On Mon, Apr 04, 2016 at 01:52:06PM +0200, Jan Kara wrote:
> Sounds like a good idea to me. I've also consulted this with Petr Mladek
> (added to CC) who is using printk_func per-cpu variable in his
> printk-from-NMI patches and he also doesn't see a problem with this.
There's a few printk() variants that do not go through this; which means
they're broken for a number of cases, including the kdb printk
redirection, this NMI stuff etc.
> I was just wondering about one thing - this way we add more early printks
> if I understand your intention right. Are we guaranteed that they happen
> only from a single CPU? Because currently there is no locking in
> early_printk() and thus we can end up writing to early console several
> messages in parallel from different CPUs. Not sure what's going to happen
> in that case...
You get lovely per char interleaving on you serial line ;-)
What I've done in the past was something like the below; that way you
only get the normal task->softirq->irq->nmi nesting, which is mostly
decipherable.
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index bfbf284e4218..c4c3269ff104 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1907,17 +1907,36 @@ struct console *early_console;
asmlinkage __visible void early_printk(const char *fmt, ...)
{
va_list ap;
+ static int print_cpu = -1;
char buf[512];
- int n;
+ int n, cpu;
if (!early_console)
return;
+ preempt_disable();
+ cpu = raw_smp_processor_id();
+ for (;;) {
+ if (READ_ONCE(print_cpu) == cpu)
+ break;
+
+ if (READ_ONCE(print_cpu) == -1 &&
+ cmpxchg(&print_cpu, -1, cpu) == -1) {
+ cpu = -1;
+ break;
+ }
+
+ cpu_relax();
+ }
+
va_start(ap, fmt);
n = vscnprintf(buf, sizeof(buf), fmt, ap);
va_end(ap);
early_console->write(early_console, buf, n);
+
+ smp_store_release(&print_cpu, cpu);
+ preempt_enable();
}
#endif
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next prev parent reply other threads:[~2016-04-04 12:46 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1459605520.git.luto@kernel.org>
2016-04-02 14:01 ` [PATCH v5 1/9] x86/head: Pass a real pt_regs and trapnr to early_fixup_exception Andy Lutomirski
2016-04-13 11:43 ` [tip:x86/asm] x86/head: Pass a real pt_regs and trapnr to early_fixup_exception() tip-bot for Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 2/9] x86/head: Move the early NMI fixup into C Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup_exception Andy Lutomirski
2016-04-02 18:39 ` Borislav Petkov
[not found] ` <20160402183919.GA2538@pd.tnic>
2016-04-02 20:13 ` Andy Lutomirski
[not found] ` <CALCETrUJVDpzNQMsY=_jWNOMer+TdW2p4wES4OBCfYU7gq3fbg@mail.gmail.com>
2016-04-02 20:47 ` Borislav Petkov
[not found] ` <20160402204752.GC2538@pd.tnic>
2016-04-02 20:58 ` Andy Lutomirski
[not found] ` <CALCETrXHR3T3PJwOWRFHTMK5WjhDyTJfaJtkiHd+g7evnqp54A@mail.gmail.com>
2016-04-04 11:52 ` Jan Kara
[not found] ` <20160404115206.GG8372@quack.suse.cz>
2016-04-04 12:46 ` Peter Zijlstra [this message]
2016-04-04 15:32 ` Andy Lutomirski
[not found] ` <CALCETrVriftUPNZ8pCQ1x9TWDHnRx8fWUvJgCQToPEOxqMLb3w@mail.gmail.com>
2016-04-04 15:36 ` Arjan van de Ven
2016-04-04 16:00 ` Peter Zijlstra
[not found] ` <20160404160042.GB3448@twins.programming.kicks-ass.net>
2016-04-04 19:38 ` Borislav Petkov
[not found] ` <20160404193803.GK351@pd.tnic>
2016-04-04 21:31 ` Andy Lutomirski
[not found] ` <CALCETrVvFTrK1pVmjnfWwwq+5P6+1ghMjh4Wwqm05d=00ejYSw@mail.gmail.com>
2016-04-04 21:40 ` Borislav Petkov
2016-04-13 11:44 ` [tip:x86/asm] x86/head: Move early exception panic code into early_fixup_exception() tip-bot for Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 4/9] x86/traps: Enable all exception handler callbacks early Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 5/9] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Andy Lutomirski
2016-04-03 8:41 ` Borislav Petkov
[not found] ` <20160403084129.GB19007@pd.tnic>
2016-04-03 13:23 ` Andy Lutomirski
[not found] ` <CALCETrUcqTx00pKYEt49QSKKBKVEx-Uv0D6dzE1-Em6Q-wkSpQ@mail.gmail.com>
2016-04-03 14:07 ` Borislav Petkov
2016-04-13 11:44 ` [tip:x86/asm] x86/paravirt: Add _safe to the read_ms()r and write_msr() PV callbacks tip-bot for Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 6/9] x86/msr: Carry on after a non-"safe" MSR access fails Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 7/9] x86/paravirt: Add paravirt_{read, write}_msr Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 8/9] x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y Andy Lutomirski
2016-04-13 11:46 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-02 14:01 ` [PATCH v5 9/9] x86/msr: Set the return value to zero when native_rdmsr_safe fails Andy Lutomirski
2016-04-02 14:24 ` [PATCH v5 0/9] Improve non-"safe" MSR access failure handling Linus Torvalds
[not found] ` <CA+55aFwi2E0A9e7krCG9dkTq7vMZnxsBwtF6_hw6QO0EVObf=g@mail.gmail.com>
2016-04-02 15:13 ` Andy Lutomirski
[not found] ` <CALCETrWP33SR5TCA-baZi8xBrHpWe=wzkuvUM=y4x_MPt1XgYg@mail.gmail.com>
2016-04-02 15:21 ` Linus Torvalds
2016-04-04 16:23 ` Borislav Petkov
[not found] ` <880eebc5dcd2ad9f310d41345f82061ea500e9fa.1459605520.git.luto@kernel.org>
2016-04-04 16:33 ` [PATCH v5 7/9] x86/paravirt: Add paravirt_{read, write}_msr David Vrabel
[not found] ` <5702974A.1030003@citrix.com>
2016-04-04 16:40 ` Andy Lutomirski
2016-04-13 11:45 ` [tip:x86/asm] x86/paravirt: Add paravirt_{read, write}_msr() tip-bot for Andy Lutomirski
2016-04-05 15:38 ` [PATCH v5 0/9] Improve non-"safe" MSR access failure handling Boris Ostrovsky
[not found] ` <20fc047d926150cb08cb9b9f2923519b07ec1a15.1459605520.git.luto@kernel.org>
2016-04-02 18:52 ` [PATCH v5 4/9] x86/traps: Enable all exception handler callbacks early Borislav Petkov
[not found] ` <20160402185227.GB2538@pd.tnic>
2016-04-02 20:16 ` Andy Lutomirski
[not found] ` <CALCETrV7PxgmhU_yXjJSugY88T8Do=vBDuG54fOFSyLp7nGcJA@mail.gmail.com>
2016-04-02 20:52 ` Borislav Petkov
[not found] ` <20160402205248.GD2538@pd.tnic>
2016-04-03 8:07 ` Borislav Petkov
[not found] ` <20160403080737.GA19007@pd.tnic>
2016-04-03 13:22 ` Andy Lutomirski
2016-04-03 13:51 ` Linus Torvalds
[not found] ` <CA+55aFw19X7PO2xd1PpUav1rSyCqUqWgi9+SA7TgjaWMaxexHQ@mail.gmail.com>
2016-04-03 13:55 ` Andy Lutomirski
[not found] ` <CALCETrX_x+tV4m3SwgCfXg9y5gia8eMhhTdUnHuXpXhnULkHRw@mail.gmail.com>
2016-04-03 14:10 ` Borislav Petkov
2016-04-03 14:17 ` Linus Torvalds
[not found] ` <20160403141041.GE19007@pd.tnic>
2016-04-04 15:47 ` Andy Lutomirski
2016-04-13 11:44 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
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