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    SubjectRe: [RFC][PATCH 12/12] perf: Collapse and fix event_function_call() users
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    On 01/11/2016 11:25 AM, Peter Zijlstra wrote:
    > There is one common bug left in all the event_function_call() users,
    > between loading ctx->task and getting to the remote_function(),
    > ctx->task can already have been changed.
    >
    > Therefore we need to double check and retry if ctx->task != current.
    >
    > Insert another trampoline specific to event_function_call() that
    > checks for this and further validates state. This also allows getting
    > rid of the active/inactive functions.
    >
    >
    > Note: Stephane, can you please look at __perf_event_enable()?
    >
    > Cc: Stephane Eranian <eranian@google.com>
    > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

    Hey Peter,

    I seem to be hitting a warning added by this patch:

    [ 258.890172] WARNING: CPU: 5 PID: 14801 at kernel/events/core.c:226 event_function+0x3a7/0x550()
    [ 258.891356] Modules linked in:[ 258.892440] CPU: 5 PID: 14801 Comm: syz-executor Not tainted 4.5.0-rc4-next-20160217-sasha-00024-g888c008-dirty #2976
    [ 258.893818] 1ffff1006c57bf07 ffff880362bdf8c0 ffffffffa43d511d ffffffff00000005
    [ 258.895071] fffffbfff60265b8 0000000041b58ab3 ffffffffafb1d490 ffffffffa43d4f85
    [ 258.896127] ffffffffa25984c0 0000000000000038 0000000000000282 ffff880362bdf898
    [ 258.897182] Call Trace:
    [ 258.897559] [<ffffffffa43d511d>] dump_stack+0x198/0x21b
    [ 258.898258] [<ffffffffa43d4f85>] ? arch_local_irq_restore+0x5f/0x5f
    [ 258.899099] [<ffffffffa25984c0>] ? is_module_text_address+0x20/0x20
    [ 258.899934] [<ffffffffa23a6851>] warn_slowpath_common+0xe1/0x160
    [ 258.900723] [<ffffffffa268cf07>] ? event_function+0x3a7/0x550
    [ 258.901473] [<ffffffffa23a6a99>] warn_slowpath_null+0x29/0x30
    [ 258.902186] [<ffffffffa268cf07>] event_function+0x3a7/0x550
    [ 258.902913] [<ffffffffa268cb60>] ? perf_event_read_event+0x3c0/0x3c0
    [ 258.906328] [<ffffffffa267d7a0>] ? free_ctx+0x70/0x70
    [ 258.907633] [<ffffffffa267d8ea>] remote_function+0x14a/0x200
    [ 258.908776] [<ffffffffa2582cb8>] generic_exec_single+0x2e8/0x5a0
    [ 258.913186] [<ffffffffa258314d>] smp_call_function_single+0x1dd/0x350
    [ 258.917536] [<ffffffffa267bc83>] task_function_call+0x123/0x160
    [ 258.938733] [<ffffffffa267dbdb>] event_function_call+0x23b/0x440
    [ 258.949427] [<ffffffffa267df7f>] _perf_event_enable+0xbf/0x100
    [ 258.952368] [<ffffffffa267e04c>] _perf_event_refresh+0x8c/0xd0
    [ 258.953776] [<ffffffffa26aa49f>] perf_ioctl+0x2af/0x870
    [ 258.963056] [<ffffffffa28fcc60>] do_vfs_ioctl+0x1b0/0x1250
    [ 258.975817] [<ffffffffa28fdd8f>] SyS_ioctl+0x8f/0xc0
    [ 258.976277] [<ffffffffad5c96c0>] entry_SYSCALL_64_fastpath+0x23/0xc1


    Thanks,
    Sasha

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