> > 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. Yeah, I do agree. Maybe it's better to go with your initial idea for 6.0, and we postpone the SB buffer pinning to a later release avoiding people to hit this issue ASAP?! > > > 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). Thanks, I'm gonna try it :) > > --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 -- Carlos Maiolino
