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    SubjectRe: [patch] warn on release_region() from irq context

    * Ingo Molnar <mingo@elte.hu> wrote:

    > ============================
    > [ BUG: illegal lock usage! ]
    > ----------------------------
    > illegal {softirq-on} -> {in-softirq} usage.
    > rcu_torture_rea/264 [HC0[0]:SC1[2]:HE1:SE0] takes:
    > (resource_lock){+-}, at: [<c0123997>] __release_region+0x37/0xf0
    > {softirq-on} state was registered at:
    > [<c0122c85>] irq_exit+0x45/0x50
    > hardirqs last enabled at: [<c011d39e>] vprintk+0x32e/0x3e0
    > softirqs last enabled at: [<c0122c85>] irq_exit+0x45/0x50
    >
    > other info that might help us debug this:
    > no locks held by rcu_torture_rea/264.
    >
    > stack backtrace:
    > [<c010432d>] show_trace+0xd/0x10
    > [<c0104347>] dump_stack+0x17/0x20
    > [<c0139078>] print_usage_bug+0x1d8/0x230
    > [<c0139436>] mark_lock+0x366/0x3a0
    > [<c0139903>] debug_lock_chain+0x493/0x1090
    > [<c013a53d>] debug_lock_chain_spin+0x3d/0x60
    > [<c0268522>] _raw_write_lock+0x32/0x1a0
    > [<c04dc158>] _write_lock+0x8/0x10
    > [<c0123997>] __release_region+0x37/0xf0
    > [<c02f5010>] floppy_release_irq_and_dma+0x140/0x200
    > [<c02f3577>] set_dor+0xc7/0x1b0
    > [<c02f65e1>] motor_off_callback+0x21/0x30
    > [<c01276c5>] run_timer_softirq+0xf5/0x1f0
    > [<c0122fc7>] __do_softirq+0x97/0x130
    > [<c01054a9>] do_softirq+0x69/0x100

    btw., Arjan discovered that this bug is not theoretical, and the
    deadlock scenario is experienced by users:

    http://i15.photobucket.com/albums/a396/johnny_blue/fedora-devel/28012006026.jpg

    Ingo
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