Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> writes: > On 3/9/20 6:40 PM, Eric W. Biederman wrote: >> Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> writes: >> >>> On 3/8/20 10:38 PM, Eric W. Biederman wrote: >>>> >>>> The cred_guard_mutex is problematic. The cred_guard_mutex is held >>>> over the userspace accesses as the arguments from userspace are read. >>>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other >> ^ over >>> >>> ... is held while waiting for the trace parent to handle PTRACE_EVENT_EXIT >>> or something? >> >> Yes. Let me see if I can phrase that better. >> >>> I wonder if we also should mention that >>> it is held while waiting for the trace parent to >>> receive the exit code with "wait"? >> >> I don't think we have to spell out the details of how it all works, >> unless that makes things clearer. Kernel developers can be expected >> to figure out how the kernel works. The critical thing is that it is >> an indefinite wait for userspace to take action. >> >> But I will look. >> >>>> threads are killed. The cred_guard_mutex is held over >>>> "put_user(0, tsk->clear_child_tid)" in exit_mm(). >>>> >>>> Any of those can result in deadlock, as the cred_guard_mutex is held >>>> over a possible indefinite userspace waits for userspace. >>>> >>>> Add exec_update_mutex that is only held over exec updating process >>> >>> Add ? >> >> Yes. That is what the change does: add exec_update_mutex. >> > > I just kind of missed the "subject" in this sentence, > like "This patch adds an exec_update_mutex that is ..." > but english is a foreign language for me, so may be okay as is. English has a lot of options. I think this is a stylistic difference. Instead of being an observer and describing what the change does: "This patch adds exec_update_mutex ..." I was being there in the moment and saying/commading what is happening: "Add exec_update_mutex ..." Using the more immdediate form ends up with more concise and clearer sentences. Every one of my writing teachers in school emphasized that point and I see the who it works when I write things. But writing is hard and I still tend toward long rambling sentences with many qualifiers that confuse and detract from the point rather than make it clear what is happening. Eric
