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    SubjectRe: [BUG] percpu misaligned allocation
    David Miller wrote:
    > From: Frederic Weisbecker <fweisbec@gmail.com>
    > Date: Thu, 18 Mar 2010 05:49:33 +0100
    >
    >> While using the lock events through perf in a sparc box, I can see
    >> the following message repeated many times:
    >>
    >> Kernel unaligned access at TPC[49357c] perf_trace_lock_acquire+0xb4/0x180
    >>
    >> It actually hangs the box as the messages are sent to a serial console.
    >>
    >> When used with perf, the trace events use a per cpu buffer allocated
    >> in kernel/trace/trace_event_perf.c, and the allocation appears to return
    >> a misaligned percpu pointer. It is aligned to 4 while it seems it
    >> requires to be aligned to 8.
    >
    > Thanks I'll take a look at this.
    >
    > RAW locks (both rwlocks and spinlocks) on sparc64 are 4-bytes
    > in size, maybe some piece of code is assuming that locks
    > are cpu word sized.
    >
    > Where is perf_trace_lock_acquire() I can't find it in Linus's
    > tree? Does it get created by some crazy macro expansion?
    >

    Yes, it's expanded by some crazy macro in include/trace/ftrace.h..

    In linus' tree, it's called ftrace_profile_lock_acquire(), and it's
    renamed to perf_trace_lock_acquire() in -tip tree by commit
    97d5a22005f38057b4bc0d95f81cd26510268794.

    #undef DECLARE_EVENT_CLASS
    #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
    static notrace void \
    ftrace_profile_templ_##call(struct ftrace_event_call *event_call, \
    proto) \
    { \
    struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
    struct ftrace_raw_##call *entry; \
    u64 __addr = 0, __count = 1; \
    unsigned long irq_flags; \
    int __entry_size; \
    int __data_size; \
    int rctx; \
    \
    ...
    }


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