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    SubjectRe: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage
    On Sat, Apr 24, 2010 at 01:35:01AM -0400, Miles Lane wrote:
    > 2.6.34-rc5-git5 with all of your patches applied.
    >
    > I reconfigured my kernel build options and got the following new issue:
    >
    > [ 2.686515] [ INFO: suspicious rcu_dereference_check() usage. ]
    > [ 2.686519] ---------------------------------------------------
    > [ 2.686523] kernel/cgroup.c:4438 invoked rcu_dereference_check()
    > without protection!
    > [ 2.686526]
    > [ 2.686527] other info that might help us debug this:
    > [ 2.686529]
    > [ 2.686532]
    > [ 2.686533] rcu_scheduler_active = 1, debug_locks = 1
    > [ 2.686537] 2 locks held by swapper/1:
    > [ 2.686540] #0: (mtd_table_mutex){+.+.+.}, at:
    > [<ffffffff812d7714>] register_mtd_blktrans+0xa2/0x25e
    > [ 2.686555] #1: (&(&blkcg->lock)->rlock){......}, at:
    > [<ffffffff811ca7bd>] blkiocg_add_blkio_group+0x29/0x7f
    > [ 2.686566]
    > [ 2.686567] stack backtrace:
    > [ 2.686572] Pid: 1, comm: swapper Not tainted 2.6.34-rc5-git5 #25
    > [ 2.686576] Call Trace:
    > [ 2.686584] [<ffffffff810642da>] lockdep_rcu_dereference+0x9d/0xa5
    > [ 2.686591] [<ffffffff8107af54>] css_id+0x3f/0x52
    > [ 2.686597] [<ffffffff811ca7cc>] blkiocg_add_blkio_group+0x38/0x7f
    > [ 2.686603] [<ffffffff811cc593>] cfq_init_queue+0xdf/0x2dc
    > [ 2.686609] [<ffffffff811bb858>] elevator_init+0xba/0xf5
    > [ 2.686616] [<ffffffff812d7046>] ? mtd_blktrans_request+0x0/0x1c
    > [ 2.686623] [<ffffffff811c0b62>] blk_init_queue_node+0x12f/0x135
    > [ 2.686629] [<ffffffff811c0b74>] blk_init_queue+0xc/0xe
    > [ 2.686635] [<ffffffff812d7777>] register_mtd_blktrans+0x105/0x25e
    > [ 2.686642] [<ffffffff818c0de9>] ? init_mtdblock+0x0/0x2c
    > [ 2.686648] [<ffffffff818c0e13>] init_mtdblock+0x2a/0x2c
    > [ 2.686656] [<ffffffff810001ef>] do_one_initcall+0x59/0x14e
    > [ 2.686663] [<ffffffff818986a6>] kernel_init+0x160/0x1ea
    > [ 2.686669] [<ffffffff81003814>] kernel_thread_helper+0x4/0x10
    > [ 2.686677] [<ffffffff8140d77c>] ? restore_args+0x0/0x30
    > [ 2.686683] [<ffffffff81898546>] ? kernel_init+0x0/0x1ea
    > [ 2.686688] [<ffffffff81003810>] ? kernel_thread_helper+0x0/0x10
    > [ 2.687683] mtdoops: mtd device (mtddev=name/number) must be supplied

    This should be covered by the patch I sent with my previous email.

    And thank you again, Miles, for all the testing!!!

    Thanx, Paul


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