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    SubjectRe: [tip:x86/urgent] x86, mce: Fix RCU lockdep from mce_poll()
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    However on my machine - I do not a see a difference ?

    I've this patch applied - and it still gives me the same error.
    (using 6aba74f2791287ec407e0f92487a725a25908067 and this patch)

    Here are my RCU config options:

    # grep RCU .config
    # RCU Subsystem
    CONFIG_TREE_PREEMPT_RCU=y
    CONFIG_PREEMPT_RCU=y
    CONFIG_RCU_TRACE=y
    CONFIG_RCU_FANOUT=64
    # CONFIG_RCU_FANOUT_EXACT is not set
    CONFIG_TREE_RCU_TRACE=y
    CONFIG_PROVE_RCU=y
    # CONFIG_PROVE_RCU_REPEATEDLY is not set
    # CONFIG_SPARSE_RCU_POINTER is not set
    # CONFIG_RCU_TORTURE_TEST is not set
    CONFIG_RCU_CPU_STALL_DETECTOR=y
    CONFIG_RCU_CPU_STALL_TIMEOUT=60
    CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE=y
    CONFIG_RCU_CPU_STALL_VERBOSE=y


    2011/3/31 tip-bot for Davidlohr Bueso <dave@gnu.org>:
    > Commit-ID:  706453b0d1fabf4dccbcffa29356d0dd6ab9afb9
    > Gitweb:     http://git.kernel.org/tip/706453b0d1fabf4dccbcffa29356d0dd6ab9afb9
    > Author:     Davidlohr Bueso <dave@gnu.org>
    > AuthorDate: Wed, 30 Mar 2011 23:13:24 -0300
    > Committer:  Ingo Molnar <mingo@elte.hu>
    > CommitDate: Thu, 31 Mar 2011 11:06:08 +0200
    >
    > x86, mce: Fix RCU lockdep from mce_poll()
    >
    > Based on the following message:
    >
    >  ===================================================
    >  [ INFO: suspicious rcu_dereference_check() usage. ]
    >  ---------------------------------------------------
    >  arch/x86/kernel/cpu/mcheck/mce.c:1628 invoked
    >  rcu_dereference_check() without protection!
    >
    >  other info that might help us debug this:
    >
    >  rcu_scheduler_active = 1, debug_locks = 1
    >  no locks held by mcelog/2350.
    >
    >  stack backtrace:
    >  Pid: 2350, comm: mcelog Tainted: G        W   2.6.37-rc1+ #7
    >  Call Trace:
    >   [<ffffffff8108e6d4>] lockdep_rcu_dereference+0xa4/0xc0
    >   [<ffffffff810189e9>] mce_poll+0xa9/0xd0
    >   [<ffffffff81160585>] do_sys_poll+0x275/0x550
    >   [<ffffffff8115f0e0>] ? __pollwait+0x0/0xf0
    >   [<ffffffff8115f1d0>] ? pollwake+0x0/0x60
    >   [<ffffffff8115f1d0>] ? pollwake+0x0/0x60
    >   [<ffffffff8130431c>] ? rcu_read_lock_held+0x2c/0x30
    >   [<ffffffff8130549a>] ? radix_tree_lookup_element+0xda/0x100
    >   [<ffffffff81121f08>] ? __do_fault+0x128/0x470
    >   [<ffffffff81100bdb>] ? filemap_fault+0xdb/0x4e0
    >   [<ffffffff810ffe75>] ? unlock_page+0x25/0x30
    >   [<ffffffff81069ddf>] ? sigprocmask+0x3f/0x100
    >   [<ffffffff8183672b>] ? _raw_spin_unlock_irq+0x2b/0x60
    >   [<ffffffff8108fefd>] ? trace_hardirqs_on_caller+0x13d/0x180
    >   [<ffffffff8108ff4d>] ? trace_hardirqs_on+0xd/0x10
    >   [<ffffffff8183672b>] ? _raw_spin_unlock_irq+0x2b/0x60
    >   [<ffffffff811608a7>] sys_ppoll+0x47/0x190
    >   [<ffffffff8108fefd>] ? trace_hardirqs_on_caller+0x13d/0x180
    >   [<ffffffff81835d39>] ? trace_hardirqs_on_thunk+0x3a/0x3f
    >   [<ffffffff810030eb>] system_call_fastpath+0x16/0x1b
    >
    > This code is simply checking the value of the pointer, and
    > therefore need not protect any actual dereferences. Replace
    > rcu_dereference_check_mce() with rcu_dereference_index_check().
    >
    > Signed-off-by: Davidlohr Bueso <dave@gnu.org>
    > Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > Cc: Zdenek Kabelac <zdenek.kabelac@gmail.com>
    > Cc: Andi Kleen <andi@firstfloor.org>
    > LKML-Reference: <1301537604.2140.21.camel@offworld>
    > Signed-off-by: Ingo Molnar <mingo@elte.hu>
    > ---
    >  arch/x86/kernel/cpu/mcheck/mce.c |    2 +-
    >  1 files changed, 1 insertions(+), 1 deletions(-)
    >
    > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
    > index 5a05ef6..a2d664f 100644
    > --- a/arch/x86/kernel/cpu/mcheck/mce.c
    > +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    > @@ -1626,7 +1626,7 @@ out:
    >  static unsigned int mce_poll(struct file *file, poll_table *wait)
    >  {
    >        poll_wait(file, &mce_wait, wait);
    > -       if (rcu_dereference_check_mce(mcelog.next))
    > +       if (rcu_dereference_index_check(mcelog.next, rcu_read_lock_sched_held()))
    >                return POLLIN | POLLRDNORM;
    >        if (!mce_apei_read_done && apei_check_mce())
    >                return POLLIN | POLLRDNORM;
    >
    --
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