linux-kernel - Re: [PATCH] rt: x86: extend signal send delay to 32 bit

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Message-ID: <20151211180532.GO6720@linutronix.de>
Date:	Fri, 11 Dec 2015 19:05:32 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Yang Shi <yang.shi@...aro.org>
Cc:	tglx@...utronix.de, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] rt: x86: extend signal send delay to 32 bit

* Yang Shi | 2015-12-10 10:58:51 [-0800]:

>When running some ptrace single step tests on x86-32 machine, the below problem
>is triggered:
>
>BUG: sleeping function called from invalid context at linux-rt/kernel/locking/rtmutex.c:917
>in_atomic(): 1, irqs_disabled(): 0, pid: 1041, name: dummy2
>INFO: lockdep is turned off.
>Preemption disabled at:[<c100326f>] do_debug+0x1f/0x1a0
>
>CPU: 10 PID: 1041 Comm: dummy2 Tainted: G        W       4.1.13-rt13 #1
>Hardware name: Intel Corporation S5520HC/S5520HC, BIOS S5500.86B.01.10.0025.030220091519 03/02/2009
> 00000000 00000000 e1811e80 c1aa8306 00000000 e1811ea8 c1080517 c1d8b2e8
> c100326f c100326f 00000411 e5b7d5b4 e1d521c4 00000005 e1811f74 e1811ec4
> c1ab0eff e1d51cc0 e5b7d180 c1081403 e5b7d180 e5b7d180 e1811ee4 c1064b5a
>Call Trace:
> [<c1aa8306>] dump_stack+0x46/0x5c
> [<c1080517>] ___might_sleep+0x137/0x220
> [<c100326f>] ? do_debug+0x1f/0x1a0
> [<c100326f>] ? do_debug+0x1f/0x1a0
> [<c1ab0eff>] rt_spin_lock+0x1f/0x80
> [<c1081403>] ? preempt_count_sub+0xb3/0x110
> [<c1064b5a>] do_force_sig_info+0x2a/0xc0
> [<c106567d>] force_sig_info+0xd/0x10
> [<c1010cff>] send_sigtrap+0x6f/0x80
> [<c10033b1>] do_debug+0x161/0x1a0
> [<c1ab2921>] debug_stack_correct+0x2e/0x35
>
>Signal send delay is just available for x86-64, x86-32 needs it too.

This is new, this was not the case earlier. New means since v4.0-rc1 which
is when 959274753857 ("x86, traps: Track entry into and exit from IST
context") got merged.
Since now ist_enter() disables preemption in any case, our hacks to
conditional_sti_ist() are pointless and could be removed.

Sebastian
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