Messages in this thread | | | Date | Mon, 27 Jun 2022 23:14:50 +0800 (CST) | From | "Liang He" <> | Subject | Re:Re: Re: [PATCH] firmware: Hold a reference for of_find_compatible_node() |
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At 2022-06-27 23:03:59, "Greg KH" <gregkh@linuxfoundation.org> wrote: >On Mon, Jun 27, 2022 at 10:51:38PM +0800, Liang He wrote: >> >> >> At 2022-06-27 22:09:43, "Greg KH" <gregkh@linuxfoundation.org> wrote: >> >On Tue, Jun 21, 2022 at 11:26:25AM +0800, Liang He wrote: >> >> In of_register_trusted_foundations(), we need to hold the reference >> >> returned by of_find_compatible_node() and then use it to call >> >> of_node_put() for refcount balance. >> >> >> >> Signed-off-by: Liang He <windhl@126.com> >> >> --- >> >> include/linux/firmware/trusted_foundations.h | 8 ++++++-- >> >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> >> >> diff --git a/include/linux/firmware/trusted_foundations.h b/include/linux/firmware/trusted_foundations.h >> >> index be5984bda592..399471c2f1c7 100644 >> >> --- a/include/linux/firmware/trusted_foundations.h >> >> +++ b/include/linux/firmware/trusted_foundations.h >> >> @@ -71,12 +71,16 @@ static inline void register_trusted_foundations( >> >> >> >> static inline void of_register_trusted_foundations(void) >> >> { >> >> + struct device_node *np = of_find_compatible_node(NULL, NULL, "tlm,trusted-foundations"); >> >> + >> >> + of_node_put(np); >> >> + if (!np) >> > >> >While this is technically correct, you are now checking to see if this >> >points to a memory location that you no longer know what it really >> >belongs to. C will let you do this, but it might be nicer to fix it up >> >properly so it doesn't look like this. >> > >> >thanks, >> > >> >greg k-h >> >> Hi,Greg KH, >> >> Thanks very much for your effort to review my patch. >> >> In fact, I have reported a commit for this kind of 'check-after-put' coding style: >> https://lore.kernel.org/all/20220617112636.4041671-1-windhl@126.com/ >> >> But I have been told to keep such style and I think the explanation is also reasonable. > >It's not very reasonable if you talk to C compiler authors. They can do >crazy things with dereferenced memory locations, including optimizing >them away entirely as they now "know" that this does not point to any >valid memory so it's an undefined thing that the compiler is being asked >to do. > >> So when I make this patch, I am indeed confused what I should write. >> >> Finally, I think it is better to be consistent with current coding style so >> I chose this 'check-after-put' style. >> >> But if you think it is better to use a normal order, i.e., check-then-put, >> I am, of cause, very happy to send a new patch for this bug and I will >> also keep to use this coding style in future. > >check and then put please. That prevents you from having to fix up this >type of thing in a few years when the compilers all start to blow up on >it. > >thanks, > >greg k-h
OK, Greg KH,
I am very happy to hear this and I will send 'check-and-put' patch tomorrow.
Thanks very much.
Liang
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