This fixes two deadlocks:

1.pcpu_alloc_mutex involved one as pointed by syzbot[1]
2.recursion deadlock.

The root cause is that we hold the bc lock during alloc_percpu, fix it
by following the pattern used by __btree_node_mem_alloc().

[1] https://lore.kernel.org/all/66f97d9a.050a0220.6bad9.001d.GAE@google.com/T/

Reported-by: syzbot+fe63f377148a6371a9db@syzkaller.appspotmail.com
Tested-by: syzbot+fe63f377148a6371a9db@syzkaller.appspotmail.com
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Factor out a version of bch2_btree_pos_to_text() that doesn't take a
pointer to a in-memory btree node, to be used for btree node scrub.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Instead of walking every extent and every backpointer it points to,
first sum up backpointers in each bucket and check for mismatches, and
only look for missing backpointers if mismatches were detected, and only
check extents in those buckets.

This is a major fsck scalability improvement, since the two backpointers
passes (backpointers -> extents and extents -> backpointers) are the
most expensive fsck passes by far.

Additionally, to speed up the upgrade for backpointer bucket gens, or in
situations when we have to rebuild alloc info, add a special case for
when no backpointers are found in a bucket - don't check each individual
backpointer (in particular, avoiding the write buffer flushes), just
recreate them.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Fix an assertion pop from the recent btree cache freelist fixes.

Fixes: baefd3f849ed ("bcachefs: btree_cache.freeable list fixes")
Reported-by: Tyler <th020394@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

btree_root entries for unknown btree IDs are created during recovery,
before reading those btree roots.

But btree_node_scan may find btree nodes with unknown btree IDs when we
haven't seen roots for those btrees.

Reported-by: syzbot+1f202d4da221ec6ebf8e@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Prefer bch2_btree_id_to_text() - it prints out the integer ID when
unknown.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

When allocating new btree nodes, we were leaving them on the freeable
list - unlocked - allowing them to be reclaimed: ouch.

Additionally, bch2_btree_node_free_never_used() ->
bch2_btree_node_hash_remove was putting it on the freelist, while
bch2_btree_node_free_never_used() was putting it back on the btree
update reserve list - ouch.

Originally, the code was written to always keep btree nodes on a list -
live or freeable - and this worked when new nodes were kept locked.

But now with the cycle detector, we can't keep nodes locked that aren't
tracked by the cycle detector; and this is fine as long as they're not
reachable.

We also have better and more robust leak detection now, with memory
allocation profiling, so the original justification no longer applies.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>