From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3zG4060bftzF0dn for ; Tue, 9 Jan 2018 18:44:05 +1100 (AEDT) Message-ID: <1515483825.541.40.camel@kernel.crashing.org> Subject: Re: Sleep in preempt_disable on powernv with 'cat /proc/cpuinfo' on v4.15 From: Benjamin Herrenschmidt To: John Sperbeck , Shriya , Michael Ellerman , linuxppc-dev@lists.ozlabs.org Date: Tue, 09 Jan 2018 18:43:45 +1100 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2018-01-08 at 21:30 -0800, John Sperbeck wrote: > The pnv_get_proc_freq() function was recently changed to call > cpufreq_get(), instead of cpufreq_quick_get(), in order to fetch > a more up-to-date value for the CPU frequency: > > cd77b5ce208c153260ed7882d8910f2395bfaabd > powerpc/powernv/cpufreq: Fix the frequency read by /proc/cpuinfo > > Unfortunately, this function is called from show_cpuinfo() in > arch/powerpc/kernel/setup-common.c with preemption disabled. The > cpufreq_get() function might do a down_read(), which can sleep. > > With CONFIG_DEBUG_KERNEL and CONFIG_DEBUG_ATOMIC_SLEEP set, a warning > like the following is generated when running 'cat /proc/cpuinfo': We could just either remove the preempt_disable completely like x86 and keep it racy, or stick a cpus_read_lock around it. I dont think we need that preempt_disable, it's definitely overkill. Michael, what do you think ? I'm keen on sync'ing with x86 here... Cheers, Ben. > BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:23 > in_atomic(): 1, irqs_disabled(): 0, pid: 16939, name: cat > CPU: 33 PID: 16939 Comm: cat Tainted: G W 4.15.0-smp-DEV #1 > Call Trace: > [c000000fef07bab0] [c000000000a32c30] dump_stack+0xb0/0xf0 (unreliable) > [c000000fef07baf0] [c0000000001343a8] ___might_sleep+0x178/0x1b0 > [c000000fef07bb70] [c000000000a50f58] down_read+0x38/0x90 > [c000000fef07bba0] [c0000000008287d0] cpufreq_get+0x50/0xc0 > [c000000fef07bbf0] [c000000000097a08] pnv_get_proc_freq+0x28/0x60 > [c000000fef07bc20] [c00000000002c554] show_cpuinfo+0x194/0x450 > [c000000fef07bcb0] [c00000000039c848] seq_read+0x1f8/0x590 > [c000000fef07bd40] [c00000000040d1d4] proc_reg_read+0xb4/0x180 > [c000000fef07bd90] [c00000000035d6a0] vfs_read+0x100/0x220 > [c000000fef07bde0] [c00000000035dc6c] SyS_read+0x6c/0x110 > [c000000fef07be30] [c00000000000b220] system_call+0x58/0x6c >