Messages in this thread |  | | From | "Bae, Chang Seok" <> | Subject | Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state | Date | Mon, 29 Mar 2021 18:14:48 +0000 |
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On Mar 26, 2021, at 09:34, Jann Horn <jannh@google.com> wrote: > On Sun, Feb 21, 2021 at 7:56 PM Chang S. Bae <chang.seok.bae@intel.com> wrote: >> >> + if (handle_xfirstuse_event(¤t->thread.fpu)) >> + return; > > What happens if handle_xfirstuse_event() fails because vmalloc() > failed in alloc_xstate_buffer()? I think that should probably kill the > task with something like force_sig() - but as far as I can tell, at > the moment, it will instead end up at die(), which should only be used > for kernel bugs.
This question was raised on v1 before [1].
In the end, people suggested to handle the failure, e.g., with tracepoints or stats. So, proposed this on the allocation site:
+ state_ptr = vmalloc(newsz); + if (!state_ptr) { + trace_x86_fpu_xstate_alloc_failed(fpu); + return -ENOMEM; + }
Also, I tried to justify this to Boris [2]:
>> Maybe it is possible to backtrack this allocation failure out of #NM >> handling. But the tracepoint can provide a clear context, although limited >> to those using it.
> Yes, add it when it is really needed. Not slapping it proactively and > hoping for any potential usage.
Let me know if you have a better way.
Thanks, Chang
[1] https://lore.kernel.org/lkml/c4669d5f-11b8-3879-562c-78a791b86229@intel.com/ [2] https://lore.kernel.org/lkml/20210204131002.GA17068@zn.tnic/
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