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SubjectRe: Re: [PATCH] mmc/core:fix mmc_sd_hw_reset oops mmc_sd_hw_reset function may be oops if the ejection of sd and the reset of sd simultaneously occur
On Fri, 1 May 2020 at 19:18, yanxiaoyong5@gmail.com
<yanxiaoyong5@gmail.com> wrote:
>
> it is a race condition,the situation as follows:
> a b
> mmc_rescan
> mmc_sd_detect
> mmc_get_card
> __mmc_reclaim_host
> card is not present __mmc_reclaim_host
> mmc_put_card wait a __mmc_release_host
> __mmc_release_host
> set b TASK_RUNNING
> mmc_sd_remove

mmc_sd_remove() calls mmc_remove_card(), which calls device_del() on
the corresponding card->dev.

That leads to ->remove() callback gets invoked for card->dev (see
mmc_blk_remove()), which ideally should clean up everything mmc block
device related. In other words, beyond this point there should be no
thread/user that can call mmc_hw_reset() (which invokes
mmc_sd_hw_reset().

> host->card =NULL
> (b starts to run)
> mmc_sd_hw_reset
> finds host->cards is NULL,then oops

So, from the above reasoning I need to ask, have you really seen the
NULL pointer exception happening? (then we need to look more closely
at mmc_blk_remove()) Or do you think there is a problem from a
code-inspection point of view?

Kind regards
Uffe

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