From mboxrd@z Thu Jan 1 00:00:00 1970 From: takahiro.akashi@linaro.org (AKASHI Takahiro) Date: Fri, 2 Oct 2015 16:56:48 +0900 Subject: [PATCH] arm64: ftrace: fix function_graph tracer panic In-Reply-To: <20151001152739.GI6963@e104818-lin.cambridge.arm.com> References: <1443581395-30088-1-git-send-email-huawei.libin@huawei.com> <560CCE91.3020407@linaro.org> <20151001152739.GI6963@e104818-lin.cambridge.arm.com> Message-ID: <560E38C0.7080409@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > Do I take this as an ack? Yes, but On 10/02/2015 12:27 AM, Catalin Marinas wrote: > On Thu, Oct 01, 2015 at 03:11:29PM +0900, AKASHI Takahiro wrote: >> On 09/30/2015 11:49 AM, Li Bin wrote: >>> When function graph tracer is enabled, the following operation >>> will trigger panic: >>> >>> mount -t debugfs nodev /sys/kernel >>> echo next_tgid > /sys/kernel/tracing/set_ftrace_filter >>> echo function_graph > /sys/kernel/tracing/current_tracer >>> ls /proc/ >>> >>> ------------[ cut here ]------------ >>> [ 198.501417] Unable to handle kernel paging request at virtual address cb88537fdc8ba316 >>> [ 198.506126] pgd = ffffffc008f79000 >>> [ 198.509363] [cb88537fdc8ba316] *pgd=00000000488c6003, *pud=00000000488c6003, *pmd=0000000000000000 >>> [ 198.517726] Internal error: Oops: 94000005 [#1] SMP >>> [ 198.518798] Modules linked in: >>> [ 198.520582] CPU: 1 PID: 1388 Comm: ls Tainted: G >>> [ 198.521800] Hardware name: linux,dummy-virt (DT) >>> [ 198.522852] task: ffffffc0fa9e8000 ti: ffffffc0f9ab0000 task.ti: ffffffc0f9ab0000 >>> [ 198.524306] PC is at next_tgid+0x30/0x100 >>> [ 198.525205] LR is at return_to_handler+0x0/0x20 >>> [ 198.526090] pc : [] lr : [] pstate: 60000145 >>> [ 198.527392] sp : ffffffc0f9ab3d40 >>> [ 198.528084] x29: ffffffc0f9ab3d40 x28: ffffffc0f9ab0000 >>> [ 198.529406] x27: ffffffc000d6a000 x26: ffffffc000b786e8 >>> [ 198.530659] x25: ffffffc0002a1900 x24: ffffffc0faf16c00 >>> [ 198.531942] x23: ffffffc0f9ab3ea0 x22: 0000000000000002 >>> [ 198.533202] x21: ffffffc000d85050 x20: 0000000000000002 >>> [ 198.534446] x19: 0000000000000002 x18: 0000000000000000 >>> [ 198.535719] x17: 000000000049fa08 x16: ffffffc000242efc >>> [ 198.537030] x15: 0000007fa472b54c x14: ffffffffff000000 >>> [ 198.538347] x13: ffffffc0fada84a0 x12: 0000000000000001 >>> [ 198.539634] x11: ffffffc0f9ab3d70 x10: ffffffc0f9ab3d70 >>> [ 198.540915] x9 : ffffffc0000907c0 x8 : ffffffc0f9ab3d40 >>> [ 198.542215] x7 : 0000002e330f08f0 x6 : 0000000000000015 >>> [ 198.543508] x5 : 0000000000000f08 x4 : ffffffc0f9835ec0 >>> [ 198.544792] x3 : cb88537fdc8ba316 x2 : cb88537fdc8ba306 >>> [ 198.546108] x1 : 0000000000000002 x0 : ffffffc000d85050 >>> [ 198.547432] >>> [ 198.547920] Process ls (pid: 1388, stack limit = 0xffffffc0f9ab0020) >>> [ 198.549170] Stack: (0xffffffc0f9ab3d40 to 0xffffffc0f9ab4000) >>> [ 198.582568] Call trace: >>> [ 198.583313] [] next_tgid+0x30/0x100 >>> [ 198.584359] [] ftrace_graph_caller+0x6c/0x70 >>> [ 198.585503] [] ftrace_graph_caller+0x6c/0x70 >>> [ 198.586574] [] ftrace_graph_caller+0x6c/0x70 >>> [ 198.587660] [] ftrace_graph_caller+0x6c/0x70 >>> [ 198.588896] Code: aa0003f5 2a0103f4 b4000102 91004043 (885f7c60) >>> [ 198.591092] ---[ end trace 6a346f8f20949ac8 ]--- >>> >>> This is because when using function graph tracer, if the traced >>> function return value is in multi regs ([0x-07]), return_to_handler typo: 0x-07 => x0-x7 and pre/post-indexed addressing stp&ldp may save add&sub instructions, but it's a matter of preference. -Takahiro AKASHI >>> may corrupt them. So in return_to_handler, the parameter regs should >>> be protected properly. >> >> You're right. we should preserve x0-x7 around a call to ftrace_return_to_handler() >> just in case they might be used as a "composite type" (ie. struct) of return value. > > Do I take this as an ack? > > I applied the patch locally and I'm going to send a pull request > tomorrow. > > Thanks. >