Messages in this thread | | | From | 河合英宏 / KAWAI,HIDEHIRO <> | Subject | RE: Re: [V4 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly | Date | Thu, 1 Oct 2015 02:04:55 +0000 |
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> On Mon, Sep 28, 2015 at 07:08:19AM +0000, 河合英宏 / KAWAI,HIDEHIRO wrote: > > > >> kernel/kexec_core.c:899:3: note: in expansion of macro 'atomic_xchg' > > > atomic_xchg(&panic_cpu, -1); > > > ^ > > > > I changed to use atomic_xchg() instead of atomic_set() in V3 > > because atomic_set() doesn't mean memory barrier. However, > > I thought again and there is no need of barrier; there is no > > problem if a competitor sees old value of panic_cpu or new one. > > So, atomic_set() is sufficient and using it will remove this warning. > > > > I will resend the fixed version later. > > So if you rely on the memory barrier; you should have also put a comment > on explaining the ordering requirements.
I don't intend to use an explicit memory barrier. There is no memory ordering requirement here. Also, atomic_set() which will be used instead of atomic_xchg() is used as a RELEASE operation, so I believe there is no problem.
Documentation/memory-barriers.txt: > The following operations are potential problems as they do _not_ imply memory > barriers, but might be used for implementing such things as RELEASE-class > operations: > > atomic_set(); > ...
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