From owner-freebsd-hackers@FreeBSD.ORG  Fri Mar  9 19:01:56 2007
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Date: Fri, 09 Mar 2007 12:37:49 -0600
From: Alan Cox <alc@cs.rice.edu>
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To: Divacky Roman <xdivac02@stud.fit.vutbr.cz>
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Cc: alc@freebsd.org, hackers@freebsd.org
Subject: Re: possibly missed wakeup in swap_pager_getpages()
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Divacky Roman wrote:

>hi
>
>  
>
[snip]

>is my analysis correct? if so, can the race be mitigated by moving the flag setting (hence
>also the locking) after the msleep()?
>
>  
>

No.  When the wakeup is performed, the VPO_SWAPINPROG flag is also 
cleared.  Both operations occur in the I/O completion handler with the 
object locked.  Thus, if the I/O completion handler runs first, the 
msleep on the page within the while loop will not occur because the 
page's VPO_SWAPINPROG  flag is already cleared.

Regards,
Alan