Re: [PATCH 3/8] mm/swap: prevent concurrent swapon on the sameS_ISBLK blockdev

[Andrew Morton]

On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <weijie.yang@xxxxxxxxxxx> wrote:

> When swapon the same S_ISBLK blockdev concurrent, the allocated two
> swap_info could hold the same block_device, because claim_swapfile()
> allow the same holder(here, it is sys_swapon function).
> 
> To prevent this situation, This patch adds swap_lock protect to ensure
> we can find this situation and return -EBUSY for one swapon call.
> 
> As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
> by holding inode->i_mutex.
> 
> This patch is just for a rare scenario, aim to correct of code.
> 

hm, OK.  Would it be saner to pass a unique `holder' to
claim_swapfile()?  Say, `p'?

Truly, I am fed up with silly swapon/swapoff races.  How often does
anyone call these things?  Let's slap a huge lock around the whole
thing and be done with it?

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