On Wed, Aug 31, 2022 at 11:43:25AM +0200, Carlos Maiolino wrote: > On Tue, Aug 30, 2022 at 08:12:17AM -0700, Darrick J. Wong wrote: > > On Tue, Aug 30, 2022 at 01:52:20PM +0200, Carlos Maiolino wrote: > > > Hi folks, > > > > > > The for-next branch of the xfsprogs repository at: > > > > > > git://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git > > > > > > has just been updated. > > > > > > This update contains the initial libxfs sync to Linux 6.0 and should be turned > > > into -rc0 once it (hopefully) gets some testing (and no complains) for more people. > > > > Wooo, welcome, new maintainer! :) > > \o/ > > > > > > Please, if any questions, let me know. > > > > For the repair deadlock fix[1], do you want me to pin the primary > > superblock buffer to the xfs_mount like Dave suggested in [2]? > > I'd rather have it pinned to the xfs_mount as it's often accessed, do you think > it is doable (you mentioned you've ran into many problems with that)? Oh, the usual problems of adding a new interface... 1. Who is responsible for setting m_sb_bp? Should libxfs_mount attach m_sb_bp? Should individual programs decide to do that if they require the functionality? Should we instead have a xfs_getsb function that returns m_sb_bp if set, or libxfs_getbufr's a new buffer and tries to cmpxchg it with the pointer? What about mkfs, which needs to libxfs_mount before it's even written anything to disk? 2. Should it be a cached buffer so that any other program (e.g. xfs_db) doing open-coded accesses of the superblock will get the same cached buffer, or should it be uncached like the kernel? If we decide on uncached, this will necessitate a full audit of xfsprogs to catch open-coded calls to libxfs_getbuf for the primary super, or else coherency problems will result. If we decide on using a cached buffer and setting it in libxfs_mount, then the part of xfs_repair that tears down the buffer cache and reinitializes it with a different hash size will also have to learn to brelse m_sb_bp before destroying the cache and re-assign it afterwards. Alternately, I suppose it could learn to rehash itself. This is a /lot/ to think about to solve one problem in one program. > I didn't have time to try to reproduce those deadlocks yet though. If you modify cache_node_get like this to make reclaim more aggressive: diff --git a/libxfs/cache.c b/libxfs/cache.c index 139c7c1b..b5e1bcf8 100644 --- a/libxfs/cache.c +++ b/libxfs/cache.c @@ -448,10 +448,10 @@ cache_node_get( /* * not found, allocate a new entry */ + priority = cache_shake(cache, priority, false); node = cache_node_allocate(cache, key); if (node) break; - priority = cache_shake(cache, priority, false); /* * We start at 0; if we free CACHE_SHAKE_COUNT we get * back the same priority, if not we get back priority+1. It's trivially reproducible with xfs_repair (do not specify -n). --D > > > > [1] https://lore.kernel.org/linux-xfs/166007921743.3294543.7334567013352169774.stgit@magnolia/ > > [2] https://lore.kernel.org/linux-xfs/20220811221541.GQ3600936@xxxxxxxxxxxxxxxxxxx/ > > -- > Carlos Maiolino
