On Fri, Feb 28, 2014 at 02:24:18PM -0500, Brian Foster wrote: > On Tue, Feb 11, 2014 at 01:07:46PM -0500, Brian Foster wrote: > > The inode chunk allocation path can lead to deadlock conditions if > > a transaction is dirtied with an AGF (to fix up the freelist) for > > an AG that cannot satisfy the actual allocation request. This code > > path is written to try and avoid this scenario, but it can be > > reproduced by running xfstests generic/270 in a loop on a 512b fs. > > > > An example situation is: > > - process A attempts an inode allocation on AG 3, modifies > > the freelist, fails the allocation and ultimately moves on to > > AG 0 with the AG 3 AGF held > > - process B is doing a free space operation (i.e., truncate) and > > acquires the AG 0 AGF, waits on the AG 3 AGF > > - process A acquires the AG 0 AGI, waits on the AG 0 AGF (deadlock) > > > > The problem here is that process A acquired the AG 3 AGF while > > moving on to AG 0 (and releasing the AG 3 AGI with the AG 3 AGF > > held). xfs_dialloc() makes one pass through each of the AGs when > > attempting to allocate an inode chunk. The expectation is a clean > > transaction if a particular AG cannot satisfy the allocation > > request. xfs_ialloc_ag_alloc() is written to support this through > > use of the minalignslop allocation args field. > > > > When using the agi->agi_newino optimization, we attempt an exact > > bno allocation request based on the location of the previously > > allocated chunk. minalignslop is set to inform the allocator that > > we will require alignment on this chunk, and thus to not allow the > > request for this AG if the extra space is not available. Suppose > > that the AG in question has just enough space for this request, but > > not at the requested bno. xfs_alloc_fix_freelist() will proceed as > > normal as it determines the request should succeed, and thus it is > > allowed to modify the agf. xfs_alloc_ag_vextent() ultimately fails > > because the requested bno is not available. In response, the caller > > moves on to a NEAR_BNO allocation request for the same AG. The > > alignment is set, but the minalignslop field is never reset. This > > increases the overall requirement of the request from the first > > attempt. If this delta is the difference between allocation success > > and failure for the AG, xfs_alloc_fix_freelist() rejects this > > request outright the second time around and causes the allocation > > request to unnecessarily fail for this AG. > > > > To address this situation, reset the minalignslop field immediately > > after use and prevent it from leaking into subsequent requests. > > > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx> > > --- > > > > v2: > > - Reset minalignslop immediately after use rather than prior to the > > subsequent request and add a comment. [dchinner] > > > > ping? Any chance to get this committed? I'm sorry, Brian, I thought I had committed it - I'll get it in the next round. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
