linux-kernel - Re: [BUG] wbsd.c: after spin_lock_bh uses spin_unlock instead spin_unlock

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Date:	Thu, 8 Oct 2009 20:35:15 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Alexander Strakh <strakh@...ras.ru>
Cc:	Pierre Ossman <pierre@...man.eu>, sdhci-devel@...ts.ossman.eu,
	Linux Kernlel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] wbsd.c: after spin_lock_bh uses spin_unlock instead
 spin_unlock_bh

On Thu, 8 Oct 2009, Alexander Strakh wrote:

> 	KERNEL_VERSION: 2.6.31
> 	DESCRIBE:
> Driver ./drivers/mmc/host/wbsd.c calls spin_lock_bh and then spin_unlock 
> instead of spin_unlock_bh:
> 
>  753 static void wbsd_request(struct mmc_host *mmc, struct mmc_request *mrq)
> ...
>  761         spin_lock_bh(&host->lock);
> ...
>  844 done:
>  845         wbsd_request_end(host, mrq);
>  846
>  847         spin_unlock_bh(&host->lock);
>  848 }
> 
> But in wsdb_request calls spin_unlock/spin_lock instead of 
> spin_unlock_bh/spin_lock_bh;
> 
>  206 static void wbsd_request_end(struct wbsd_host *host, struct mmc_request 
> ...
>  230         spin_unlock(&host->lock);
>  231         mmc_request_done(host->mmc, mrq);
>  232         spin_lock(&host->lock);
>  233 }

And where exactly you see a bug?

wbsd_request_end() can be called in the following ways:

- through wbsd_finish_data() from tasklet (therefore no need to disable 
  tasklets there)
- from wbsd_request() directly. The sequence here is

	spin_lock_bh(&host->lock);
	...
	wbsd_request_end(host, mrq);
		spin_unlock(&host->lock);
		....
		spin_lock(&host->lock);		
	spin_unlock_bh(&host->lock);	

  So the whole thing runs with tasklets disabled, no matter what you do 
  with the host->lock, and they are only enabled at the very end of 
  wbsd_request()

So, what exact problem scenario do you see here?

-- 
Jiri Kosina
SUSE Labs, Novell Inc.

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