The new guard(), scoped_guard() allow for more natural code.
Some of the uses with creative flow control have been left.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
If path->should_be_locked is true, that means user code (of the btree
API) has seen, in this transaction, something guarded by the node this
path has locked, and we have to keep it locked until the end of the
transaction.
Assert that we're not violating this; should_be_locked should also be
cleared only in _very_ special situations.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We're adding new should_be_locked assertions: it's going to be illegal
to unlock a should_be_locked path when trans->locked is true.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Small additional optimization over the previous patch, bringing us
closer to the original behaviour, except when we need to clone to avoid
a transaction restart.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
btree_path_get_locks, on failure, shouldn't unlock if we're not issuing
a transaction restart: we might drop locks we're not supposed to (if
path->should_be_locked is set).
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
- Convert to a 'fs_str' tracepoint that just emits as a string: this
lets us build up the tracepoint with a printbuf, using our pretty
printers, and they're much easier to manage
- Include locks_held, before and after
- Include the btree node pointer we failed on (error pointer, null, or
real node)
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Don't put btree locking asserts behind CONFIG_BCACHEFS_DEBUG, put them
behind a module parameter.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
bch2_print_string_as_lines() is a low level helper that allows messages
longer than 1k to be printed without truncation.
But we should always be printing with the helpers that take a filesystem
object, if we're in fsck they direct output to the userspace process
controlling fsck instead of the dmesg log.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
In debug mode, we save the call stack on transaction restart - but
there's no locking, so we can't touch it if we're issuing the restart
from another thread.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The transaction is going to abort, so there will be no cycle involving
this transaction anymore.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
When the cycle doesn't involve the initiator of the cycle detection,
we might choose a transaction that is not involved in the cycle to abort.
It shouldn't be that since it won't break the cycle, this patch
therefore chooses the transaction in the cycle to abort.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This patch introduces a helper function called lock_graph_pop_from,
it pops the graph from i.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
If the transaction chose itself as a victim before and restarted, it
might request a no fail lock request this time. But it might be added to
others' lock graph and be chose as the victim again, it's no longer safe
without additional check. We can also convert the cycle detector to be
fully RCU-based to solve that unsoundness, but the latency added to trans_put
and additional memory required may not worth it.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This reverts commit 62448afee7.
six_lock_tryupgrade fails only if there is an intent lock held,
it won't fail no matter how many read locks are held.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
New helper for dropping all write locks; which is distinct from the
helper the transaction commit path uses, which is faster and only
touches updates.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
If the btree_path's lock seq is wrong, the next bch2_trans_relock()
operation is guaranteed to fail and we take an unnecessary transaction
restart.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Add a new helper to disable lockdep tracking entirely for a given class.
This is needed for bcachefs, which takes too many btree node locks for
lockdep to track. Instead, we have a single lockdep_map for "btree_trans
has any btree nodes locked", which makes more since given that we have
centralized lock management and a cycle detector.
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Add a field for tracking whether a transaction object holds btree locks,
and assertions to verify state.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
In the key cache fill path, we use path_upgrade() on a path that isn't
uptodate yet but should be locked.
This change makes bch2_btree_path_upgrade() slightly looser so we can
use it in key cache upgrade, instead of the __ version.
Also, make the related assert - that path->uptodate implies nodes_locked
- slightly clearer.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
dropping read locks in bch2_btree_node_lock_write_nofail() dates from
before we had the cycle detector; we can now tell the cycle detector
directly when taking a lock may not fail because we can't handle
transaction restarts.
This is needed for adding should_be_locked asserts.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
If a path doesn't have any active references, we shouldn't downgrade it;
it'll either be reused, possibly with intent refs again, or dropped at
bch2_trans_begin() time.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
- Some tweaks to greatly reduce locking overhead for the list of btree
transactions, so that it can always be enabled: leave btree_trans
objects on the list when they're on the percpu single item freelist,
and only check for duplicates in the same process when
CONFIG_BCACHEFS_DEBUG is enabled
- don't zero out the full btree_trans() unless we allocated it from
the mempool
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Upcoming patches are going to be changing trans->paths to a
reallocatable buffer. We need to guard against use after free when it's
used by other threads; this introduces RCU protection to those paths and
changes them to check for trans->paths == NULL
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
path->idx is now a code smell: we should be using path_idx_t, since it's
stable across btree path reallocation.
This is also a bit faster, using the same loop counter vs. fetching
path->idx from each path we iterate over.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
These were for extra info in tracepoints for debugging a specialized
issue - we do not want to bloat btree_path for this, at least in release
builds.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
In the CI, we're seeing tests failing due to excessive would_deadlock
transaction restarts - the tracepoint now includes the lock cycle that
occured.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
