lkml.org 
[lkml]   [2008]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch 2.6.28-rc2] at91_mci: workaround lockdep
David Brownell :
> From: David Brownell <dbrownell@users.sourceforge.net>
>
> Lockdep reported a problem in the at91_mci driver ... in this case, the
> issue is with lockdep, not with the driver. A trimmed stack dump, from
> trying to boot with root on MMC, shows:
>
> WARNING: at kernel/lockdep.c:2195 trace_hardirqs_on_caller+0xf4/0x170()
> Modules linked in:
> [<c005bc98>] (trace_hardirqs_on+0x0/0x18) from [<c0213bf4>] (_spin_unlock_irq+0x2c/0x3c)
> [<c0213bc8>] (_spin_unlock_irq+0x0/0x3c) from [<c0029a88>] (flush_dcache_page+0x114/0x144)
> [<c0029974>] (flush_dcache_page+0x0/0x144) from [<c019b034>] (at91_mci_irq+0x150/0x414)
> [<c019aee4>] (at91_mci_irq+0x0/0x414) from [<c0066c5c>] (handle_IRQ_event+0x2c/0x6c)
> [<c0066c30>] (handle_IRQ_event+0x0/0x6c) from [<c0068a60>] (handle_level_irq+0x108/0x124)
> [<c0068958>] (handle_level_irq+0x0/0x124) from [<c0022064>] (__exception_text_start+0x64/0x90)
>
> When __flush_dcache_aliases() returns -- inlined into flush_dcache_page(),
> above -- it re-enables IRQs ... since that evidently may only be called with
> IRQs enabled. That's OK since the (unshared) IRQ handler doesn't ask for IRQs
> to be disabled. Except ... that lockdep went and disabled them, then went on
> to complains about the breakage *it* caused!
>
> Workaround: depend on LOCKDEP=n ... and for paranoia, disable IRQF_SHARED
> for this interrupt. (At the hardware level, this is dedicated to MCI, so
> there's never a need for multiple handlers.)
>
> Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

> ---
> An alternate fix might be to have ARM dcache mmap locking save and restore
> the IRQ flags ... but there are several such "can't run with IRQs disabled"
> restrictions scattered through that code, with no rationales commented. Or
> stop lockdep from mucking with IRQ flags; probably not any time soon!
>
> So for now, this seems to be the best "solution" available...
>
> drivers/mmc/host/Kconfig | 1 +
> drivers/mmc/host/at91_mci.c | 3 +--
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> --- a/drivers/mmc/host/Kconfig
> +++ b/drivers/mmc/host/Kconfig
> @@ -99,6 +99,7 @@ config MMC_AU1X
> config MMC_AT91
> tristate "AT91 SD/MMC Card Interface support"
> depends on ARCH_AT91
> + depends on LOCKDEP=n
> help
> This selects the AT91 MCI controller.
>
> --- a/drivers/mmc/host/at91_mci.c
> +++ b/drivers/mmc/host/at91_mci.c
> @@ -1081,8 +1081,7 @@ static int __init at91_mci_probe(struct
> * Allocate the MCI interrupt
> */
> host->irq = platform_get_irq(pdev, 0);
> - ret = request_irq(host->irq, at91_mci_irq, IRQF_SHARED,
> - mmc_hostname(mmc), host);
> + ret = request_irq(host->irq, at91_mci_irq, 0, mmc_hostname(mmc), host);
> if (ret) {
> dev_dbg(&pdev->dev, "request MCI interrupt failed\n");
> goto fail0;
>

Thanks, regards,
--
Nicolas Ferre



\
 
 \ /
  Last update: 2008-11-17 10:31    [W:0.077 / U:4.280 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site