Messages in this thread | | | Date | Thu, 7 Sep 2017 18:36:31 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages |
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(Cc Tony, Fenghua, Benjamin, Paul, Michael)
a brief description:
original patch set: lkml.kernel.org/r/1504729681-3504-1-git-send-email-deller@gmx.de
start of this discussion: lkml.kernel.org/r/20170907075653.GA533@jagdpanzerIV.localdomain
basically we are looking at possibilities to make %pF/%pS differences less disturbing. Helge has discovered a number of wrong usages in the kernel and has fixed the currently existing call sites; the question is what we can do to avoid this type of the patch sets in the future? /* assuming that no one reads printk documentation */
Hopefully you guys can help.
On (09/07/17 11:12), Helge Deller wrote: [..] > > - ptr = dereference_function_descriptor(ptr); > > + ptr = __dereference_function_descriptor(ptr); > > This is not needed. > All affected arches (ia64, ppc64, parisc64) already call > probe_kernel_address() inside their dereference_function_descriptor() function. > So this patch just adds unnecessary overhead for all arches.
good, thanks. honestly, I obviously didn't check what each platform does. guilty! sort of.
> > ... here is a question, does function descriptor belong to a special > > section? can we check that supplied ptr belongs to a descriptor section > > and avoid dereference_function_descriptor() if it doesn't? (just fall > > through directly to symbol_string() in this case). is this possible? > > I think theoretically yes. > On parisc ptr does *not* point to any code segment, and most likely it > points to the .data segment. I don't know if that's the case for ia64 and > ppc64 too. > I can look into adding such check-code, but even then the warning will > only show up if you run on ia64, ppc64 and parisc64.
ok. personally I think that we need to start doing "does ptr belong to descriptor segment/section/etc" thing and skip dereference_function_descriptor() when it doesn't. [well, where possible. hopefully on every affected platform... if this problem actually bothers any one]. that seems like the way to fix the root cause of the problem. because it's you, Petr and may be 7 more guys who knows the difference between %pF/%pS. no one else has any idea at all. and no one actually reads the printk() documentation, let's be real :)
-ss
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