Re: kern/39206: ffs um_lock handling isn't great

[David Holland <dholland-bugs%netbsd.org@localhost>]

On Fri, Jul 25, 2008 at 02:15:00PM +0000, Simon Burge wrote:
 >         One example pointed out by pooka@ is at the top of
 >         ffs_alloccg().  It appears that once the free block check at
 >         the top of this function succeeds, this function isn't allowed
 >         to fail.  This is noted in the "XXX fvdl mapsearch ..." comment
 >         further down.  This function is entered with um_lock held, and
 >         once the free block check has passed um_lock is dropped.  This
 >         then allows another thread to reach the same point, and could
 >         lead to problems if there was only one block free in the CG
 >         before the first thread get there.
 > 
 >         This PR is entered as priority "medium" and not "high" since no
 >         actual problems have been observed in practice yet.

Unless this is the source of those occasional "ffs_alloccg: map
corrupted" panics...

-- 
David A. Holland
dholland%netbsd.org@localhost