Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 29 Apr 2020 20:50:15 -0700 | Subject | Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1 |
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On Wed, Apr 29, 2020 at 8:41 PM Jann Horn <jannh@google.com> wrote: > > | So a ptrace() user (or [...] wouldn't even see the impossible EAGAIN error. > > So I assumed you explicitly wanted ptrace() to restart, too. I was > just pointing out that that didn't make sense to me.
I'm actually ok with the restart option, simply because I continue to maintain that the program is buggy. "Anything goes".
To not be buggy, the program needs to install a SIGCHLD handler so that it can reap its (pseudo-)children.
At which point it doesn't actually make any difference whether we fix the kernel or not, because then the non-buggy program will just work - even with a non-modified kernel.
Honestly, the main argument for the kernel doing anything different at all is that from a user-mode perspective, silently hanging in the kernel waiting for something to happen is likely the least easy to debug.
But if you do a return to user space - even if it's to just rinse and repeat - it's at least not "silent" any more, even if the main noise it makes is just to waste 100% CPU time. At least that's a big hint to somebody to take a look.
But yes, we can make ptrace() - and _only_ ptrace() - then not repeat, and return a new error code that it has never returned before. Like EAGAIN. Mainly because in that case we're only breaking semantics of something that was already broken - unlike "write()", which has perfectly well-defined semantics and wasn't broken.
Linus
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