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Thu, 26 Sep 2024 03:12:39 -0700 (PDT) Received: from localhost ([183.226.245.34]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20af172207csm35630685ad.67.2024.09.26.03.12.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Sep 2024 03:12:38 -0700 (PDT) From: chenqiwu X-Google-Original-From: chenqiwu Date: Thu, 26 Sep 2024 18:12:35 +0800 To: Oleg Nesterov Cc: chenqiwu , corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org, paulmck@kernel.org, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v4 2/2] arm64: show signal info for global init Message-ID: <20240926101235.GA3662@rlk> References: <20240924074341.37272-1-qiwu.chen@transsion.com> <20240924074341.37272-2-qiwu.chen@transsion.com> <20240924183634.GB17395@redhat.com> <20240925035440.GA2941@rlk> <20240925120546.GA26882@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240925120546.GA26882@redhat.com> X-Rspam-User: X-Stat-Signature: wi8zyrrpd983w6hy3ysb8x4bwtwtpnb1 X-Rspamd-Queue-Id: 82774120013 X-Rspamd-Server: rspam11 X-HE-Tag: 1727345560-14371 X-HE-Meta: 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 auY4KWMD csfvcbqF1B1IgVZ2MgNI+H5A8857fn0/kNvObSkp4Q8HYmUo0DJ5aubSJynBP/VJOvyU6xXiPmyDWN+Fgm8gUsDQDvv/f8eZfp2k9jC8IhAqMiGuVqBfDuiu2+Yrwho3c7ZYZ7hkHYY/D7YFfOcjz62moHXzgHEs7emcoU2udNHv9ksieVqKXjmoau2rxp8rONFzuxfDSrOD9IiPohDLFFQYolgtFr2YPOnmqYUn4PDc3yUWemMSpQ+q5T9kipEFmE0oULLTYh5sOkq8zYGt9iSB5MJZ2UxfBo+BSV9L+fpk0FLKDdv0bUd4SCVw2YASUhDiSg7oo/5T5tKqYGJI8lSHGuJmRAjDGBzlDwuDwf+ZEzdL7CTb4vKlzGIdDXtfTBuRMTyvEThlnQ+s= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 25, 2024 at 02:05:47PM +0200, Oleg Nesterov wrote: > > > > > Yes, this patch just try to bypass the show_unhandled_signals and > > __ratelimit() checks for the global init. > > I think the changelog should explain this. > Sure, I will explain this in the changelog of patch v5 if someone else would ACK this patch. > But this doesn't look right to me, see below. > > > > OTOH. The is_global_init() check in unhandled_signal() (which predates the git > > > history) doesn't look right to me. If init has a handler for, say, SIGSEGV, why > > > should the kernel complain? I need to recheck this logic... > > > > > I think the orignal logic is the signal sent to the global init is > > regarded as unhandled becuase it has SIGNAL_UNKILLABLE feature. > > And? How does this relate to SIGNAL_UNKILLABLE? Again, this check predates > the git history and the SIGNAL_UNKILLABLE feature. And SIGNAL_UNKILLABLE > has no effect in this case, see force_sig_info_to_task(). > Thanks for your explaination! For the report on ARM64 KVM, the signal sent to the global init by arm4_force_sig() and the global init do_exit by get_signal(). However, it doesn't show signal info due to show_unhandled_signals check, because the initial value of show_unhandled_signals is 0 which can be adjusted by /proc/sys/debug/exception-trace in root mode. In ARM64 productive environment, the default value of show_unhandled_signals is set to 0 in case of show_unhandled_signals storms, and the debuggers cannot adjust it dynamically by shell in non-root mode. Considering the minor case of kill init, this change won't have any side effect. Let's to see the ARM64 maintainers if really like it :) Thanks Qiwu