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Date: Thu, 23 Jun 2022 16:55:05 -0500 From: "Eric W. Biederman" <ebiederm@...ssion.com> To: Alexander Gordeev <agordeev@...ux.ibm.com> Cc: Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org, mingo@...nel.org, bigeasy@...utronix.de, Peter Zijlstra <peterz@...radead.org>, Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>, "Robert O'Callahan" <roc@...nos.co>, Kyle Huey <khuey@...nos.co>, Keno Fischer <keno@...iacomputing.com> Subject: Re: [PATCH 0/3] ptrace: Stop supporting SIGKILL for PTRACE_EVENT_EXIT Alexander Gordeev <agordeev@...ux.ibm.com> writes: > On Wed, Jun 22, 2022 at 11:43:37AM -0500, Eric W. Biederman wrote: >> Recently I had a conversation where it was pointed out to me that >> SIGKILL sent to a tracee stropped in PTRACE_EVENT_EXIT is quite >> difficult for a tracer to handle. >> >> Keeping SIGKILL working for anything after the process has been killed >> is also a real pain from an implementation point of view. >> >> So I am attempting to remove this wart in the userspace API and see >> if anyone cares. > > Hi Eric, > > With this series s390 hits the warning exactly same way. Is that expected? Yes. I was working on this before I got your mysterious bug report. I included you because I am including everyone I know who deals with the userspace side of this since I am very deliberately changing the user visible behavior of PTRACE_EVENT_EXIT. I am going to start seeing if I can find any possible explanation for your regression report. Since I don't have much to go on I expect I will have to revert the last change in my ptrace_stop series that apparently triggers the WARN_ON you reported. I really would have expected the WARN_ON to be triggered in the patch in which it was introduced, not the final patch in the series. To the best of my knowledge changing PTRACE_EVENT_EXIT is both desirable from a userspace semantics standpoint and from a kernel implementation standpoint. If someone knows any differently and depends upon sending SIGKILL to processes in PTRACE_EVENT_EXIT to steal the process away from the tracer I would love to hear about that case. Eric
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