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    Subject[PATCH] sdhci: Fix potential spinlock recursion
    I noticed this bug while working on a driver that is derived
    from the SDHCI driver:

    BUG: spinlock recursion on CPU#0, swapper/0
    lock: df890668, .magic: dead4ead, .owner: swapper/0, .owner_cpu: 0
    Call Trace:
    [c04b5c50] [c0008b2c] show_stack+0x4c/0x16c (unreliable)
    [c04b5c90] [c0193aa8] spin_bug+0x7c/0xc4
    [c04b5cb0] [c0193dcc] _raw_spin_lock+0xb4/0xb8
    [c04b5cc0] [c035baf4] _spin_lock+0x10/0x20
    [c04b5cd0] [c02a8d60] esdhc_irq+0x20/0x210
    [c04b5cf0] [c00665c0] handle_IRQ_event+0x5c/0xb0
    [c04b5d10] [c0068708] handle_level_irq+0xa8/0x144
    [c04b5d30] [c000684c] do_IRQ+0xac/0xec
    [c04b5d50] [c0014f24] ret_from_except+0x0/0x14
    --- Exception: 501 at __delay+0x34/0x74
    LR = esdhc_reset+0xa4/0x114
    [c04b5e10] [c0480000] empty_zero_page+0x0/0x1000 (unreliable)
    [c04b5e30] [c02a9150] esdhc_tasklet_card+0x104/0x148
    [c04b5e50] [c003cabc] tasklet_action+0x78/0xfc
    [c04b5e60] [c003cbc4] __do_softirq+0x84/0x124
    [c04b5e90] [c00065dc] do_softirq+0x58/0x5c
    [c04b5ea0] [c003ca40] irq_exit+0x94/0x98
    [c04b5eb0] [c0006850] do_IRQ+0xb0/0xec
    [c04b5ed0] [c0014f24] ret_from_except+0x0/0x14
    --- Exception: 501 at cpu_idle+0xa0/0xec
    LR = cpu_idle+0xa0/0xec
    [c04b5f90] [c0009d14] cpu_idle+0x50/0xec (unreliable)
    [c04b5fb0] [c035c000] __got2_end+0x58/0x68
    [c04b5fc0] [c04468fc] start_kernel+0x1a4/0x228
    [c04b5ff0] [00003438] 0x3438

    This happens because plain spin_lock() won't protect us from
    softirqs (tasklets). So in the sdhci interrupt handler we must
    grab the _irq version of the lock.

    Note that the _irqsave version isn't mandatory here because
    a) we aren't trying to protect ourselves from another hardirq, and
    b) the sdhci driver requests irqs with IRQF_SHARED flag, and that
    guarantees that we'll get a huge warning if anyone will try to
    request the same interrupt with IRQF_DISABLED flag, since
    IRQF_SHARED | IRQF_DISABLED is guaranteed to be broken anyway.

    Briefly looking into other mmc hosts I don't see any problems
    with them, so the fix goes for the sdhci driver only.

    Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
    ---
    drivers/mmc/host/sdhci.c | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
    index 4d010a9..5248041 100644
    --- a/drivers/mmc/host/sdhci.c
    +++ b/drivers/mmc/host/sdhci.c
    @@ -1363,7 +1363,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
    u32 intmask;
    int cardint = 0;

    - spin_lock(&host->lock);
    + spin_lock_irq(&host->lock);

    intmask = readl(host->ioaddr + SDHCI_INT_STATUS);

    @@ -1424,7 +1424,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)

    mmiowb();
    out:
    - spin_unlock(&host->lock);
    + spin_unlock_irq(&host->lock);

    /*
    * We have to delay this as it calls back into the driver.
    --
    1.5.6.5

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