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From: Daniel Mack <zonque@gmail.com>
To: Balaji T K <balajitk@ti.com>
Cc: Linux MMC List <linux-mmc@vger.kernel.org>,
	"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>
Subject: omap_hsmmc: race between omap_hsmmc_start_command() and DMA callback
Date: Thu, 18 Jul 2013 18:06:19 +0200	[thread overview]
Message-ID: <51E8127B.9090903@gmail.com> (raw)

Hi,

I'm facing a NULL pointer dereference in omap_hsmmc_start_command() on
an AM33xx board running 3.11-rc1 (DMA enabled).

A quick debug session showed that DMA engine timing leads to a very
reproducable race condition. In omap_hsmmc_request(), we have:

        host->mrq = req;
        omap_hsmmc_prepare_data()
		omap_hsmmc_start_dma_transfer()
			tx->callback = omap_hsmmc_dma_callback;

	[*]

	omap_hsmmc_start_command()
		if (cmd == host->mrq->stop) [<-- oops]
			...

It turns out that omap_hsmmc_dma_callback() (which sets host->mrq =
NULL) is entered just after the DMA submission, and *before*
omap_hsmmc_start_command() is called, consequently leading to an Oops.

I can debug this in more depth, but maybe someone has an idea already?


Thanks,
Daniel


             reply	other threads:[~2013-07-18 16:06 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-18 16:06 Daniel Mack [this message]
2013-07-18 16:30 ` omap_hsmmc: race between omap_hsmmc_start_command() and DMA callback Balaji T K

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