bcachefs fixes for 6.14-rc2

- add a SubmittingPatches to clarify that patches submitted for bcachefs
   do, in fact, need to be tested
 - discard path now correctly issues journal flushes when needed, this
   fixes performance issues when the filesystem is nearly full and we're
   bottlenecked on copygc
 - fix a bug that could cause the pending rebalance work accounting to be
   off when devices are being onlined/offlined; users should report if
   they are still seeing this
 - and a few more trivial ones
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Merge tag 'bcachefs-2025-02-06.2' of git://evilpiepirate.org/bcachefs

Pull bcachefs fixes from Kent Overstreet:
 "Nothing major, things continue to be fairly quiet over here.

   - add a SubmittingPatches to clarify that patches submitted for
     bcachefs do, in fact, need to be tested

   - discard path now correctly issues journal flushes when needed, this
     fixes performance issues when the filesystem is nearly full and
     we're bottlenecked on copygc

   - fix a bug that could cause the pending rebalance work accounting to
     be off when devices are being onlined/offlined; users should report
     if they are still seeing this

   - and a few more trivial ones"

* tag 'bcachefs-2025-02-06.2' of git://evilpiepirate.org/bcachefs:
  bcachefs: bch2_bkey_sectors_need_rebalance() now only depends on bch_extent_rebalance
  bcachefs: Fix rcu imbalance in bch2_fs_btree_key_cache_exit()
  bcachefs: Fix discard path journal flushing
  bcachefs: fix deadlock in journal_entry_open()
  bcachefs: fix incorrect pointer check in __bch2_subvolume_delete()
  bcachefs docs: SubmittingPatches.rst

Documentation/filesystems/bcachefs/SubmittingPatches.rst

@@ -0,0 +1,98 @@
+Submitting patches to bcachefs:
+===============================
+
+Patches must be tested before being submitted, either with the xfstests suite
+[0], or the full bcachefs test suite in ktest [1], depending on what's being
+touched. Note that ktest wraps xfstests and will be an easier method to running
+it for most users; it includes single-command wrappers for all the mainstream
+in-kernel local filesystems.
+
+Patches will undergo more testing after being merged (including
+lockdep/kasan/preempt/etc. variants), these are not generally required to be
+run by the submitter - but do put some thought into what you're changing and
+which tests might be relevant, e.g. are you dealing with tricky memory layout
+work? kasan, are you doing locking work? then lockdep; and ktest includes
+single-command variants for the debug build types you'll most likely need.
+
+The exception to this rule is incomplete WIP/RFC patches: if you're working on
+something nontrivial, it's encouraged to send out a WIP patch to let people
+know what you're doing and make sure you're on the right track. Just make sure
+it includes a brief note as to what's done and what's incomplete, to avoid
+confusion.
+
+Rigorous checkpatch.pl adherence is not required (many of its warnings are
+considered out of date), but try not to deviate too much without reason.
+
+Focus on writing code that reads well and is organized well; code should be
+aesthetically pleasing.
+
+CI:
+===
+
+Instead of running your tests locally, when running the full test suite it's
+prefereable to let a server farm do it in parallel, and then have the results
+in a nice test dashboard (which can tell you which failures are new, and
+presents results in a git log view, avoiding the need for most bisecting).
+
+That exists [2], and community members may request an account. If you work for
+a big tech company, you'll need to help out with server costs to get access -
+but the CI is not restricted to running bcachefs tests: it runs any ktest test
+(which generally makes it easy to wrap other tests that can run in qemu).
+
+Other things to think about:
+============================
+
+- How will we debug this code? Is there sufficient introspection to diagnose
+  when something starts acting wonky on a user machine?
+
+  We don't necessarily need every single field of every data structure visible
+  with introspection, but having the important fields of all the core data
+  types wired up makes debugging drastically easier - a bit of thoughtful
+  foresight greatly reduces the need to have people build custom kernels with
+  debug patches.
+
+  More broadly, think about all the debug tooling that might be needed.
+
+- Does it make the codebase more or less of a mess? Can we also try to do some
+  organizing, too?
+
+- Do new tests need to be written? New assertions? How do we know and verify
+  that the code is correct, and what happens if something goes wrong?
+
+  We don't yet have automated code coverage analysis or easy fault injection -
+  but for now, pretend we did and ask what they might tell us.
+
+  Assertions are hugely important, given that we don't yet have a systems
+  language that can do ergonomic embedded correctness proofs. Hitting an assert
+  in testing is much better than wandering off into undefined behaviour la-la
+  land - use them. Use them judiciously, and not as a replacement for proper
+  error handling, but use them.
+
+- Does it need to be performance tested? Should we add new peformance counters?
+
+  bcachefs has a set of persistent runtime counters which can be viewed with
+  the 'bcachefs fs top' command; this should give users a basic idea of what
+  their filesystem is currently doing. If you're doing a new feature or looking
+  at old code, think if anything should be added.
+
+- If it's a new on disk format feature - have upgrades and downgrades been
+  tested? (Automated tests exists but aren't in the CI, due to the hassle of
+  disk image management; coordinate to have them run.)
+
+Mailing list, IRC:
+==================
+
+Patches should hit the list [3], but much discussion and code review happens on
+IRC as well [4]; many people appreciate the more conversational approach and
+quicker feedback.
+
+Additionally, we have a lively user community doing excellent QA work, which
+exists primarily on IRC. Please make use of that resource; user feedback is
+important for any nontrivial feature, and documenting it in commit messages
+would be a good idea.
+
+[0]: git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
+[1]: https://evilpiepirate.org/git/ktest.git/
+[2]: https://evilpiepirate.org/~testdashboard/ci/
+[3]: linux-bcachefs@vger.kernel.org
+[4]: irc.oftc.net#bcache, #bcachefs-dev

Documentation/filesystems/bcachefs/index.rst

@@ -9,4 +9,5 @@ bcachefs Documentation
    :numbered:
 
    CodingStyle
+   SubmittingPatches
    errorcodes

MAINTAINERS

@@ -3954,6 +3954,7 @@ M:	Kent Overstreet <kent.overstreet@linux.dev>
 L:	linux-bcachefs@vger.kernel.org
 S:	Supported
 C:	irc://irc.oftc.net/bcache
+P:      Documentation/filesystems/bcachefs/SubmittingPatches.rst
 T:	git https://evilpiepirate.org/git/bcachefs.git
 F:	fs/bcachefs/
 F:	Documentation/filesystems/bcachefs/

fs/bcachefs/alloc_background.c

@@ -1803,7 +1803,6 @@ struct discard_buckets_state {
 	u64		open;
 	u64		need_journal_commit;
 	u64		discarded;
-	u64		need_journal_commit_this_dev;
 };
 
 static int bch2_discard_one_bucket(struct btree_trans *trans,
@@ -1827,11 +1826,11 @@ static int bch2_discard_one_bucket(struct btree_trans *trans,
 		goto out;
 	}
 
-	if (bch2_bucket_needs_journal_commit(&c->buckets_waiting_for_journal,
-			c->journal.flushed_seq_ondisk,
-			pos.inode, pos.offset)) {
-		s->need_journal_commit++;
-		s->need_journal_commit_this_dev++;
+	u64 seq_ready = bch2_bucket_journal_seq_ready(&c->buckets_waiting_for_journal,
+						      pos.inode, pos.offset);
+	if (seq_ready > c->journal.flushed_seq_ondisk) {
+		if (seq_ready > c->journal.flushing_seq)
+			s->need_journal_commit++;
 		goto out;
 	}
 
@@ -1865,23 +1864,24 @@ static int bch2_discard_one_bucket(struct btree_trans *trans,
 		discard_locked = true;
 	}
 
-	if (!bkey_eq(*discard_pos_done, iter.pos) &&
-	    ca->mi.discard && !c->opts.nochanges) {
-		/*
-		 * This works without any other locks because this is the only
-		 * thread that removes items from the need_discard tree
-		 */
-		bch2_trans_unlock_long(trans);
-		blkdev_issue_discard(ca->disk_sb.bdev,
-				     k.k->p.offset * ca->mi.bucket_size,
-				     ca->mi.bucket_size,
-				     GFP_KERNEL);
-		*discard_pos_done = iter.pos;
+	if (!bkey_eq(*discard_pos_done, iter.pos)) {
 		s->discarded++;
+		*discard_pos_done = iter.pos;
 
-		ret = bch2_trans_relock_notrace(trans);
-		if (ret)
-			goto out;
+		if (ca->mi.discard && !c->opts.nochanges) {
+			/*
+			 * This works without any other locks because this is the only
+			 * thread that removes items from the need_discard tree
+			 */
+			bch2_trans_unlock_long(trans);
+			blkdev_issue_discard(ca->disk_sb.bdev,
+					     k.k->p.offset * ca->mi.bucket_size,
+					     ca->mi.bucket_size,
+					     GFP_KERNEL);
+			ret = bch2_trans_relock_notrace(trans);
+			if (ret)
+				goto out;
+		}
 	}
 
 	SET_BCH_ALLOC_V4_NEED_DISCARD(&a->v, false);
@@ -1929,6 +1929,9 @@ static void bch2_do_discards_work(struct work_struct *work)
 				   POS(ca->dev_idx, U64_MAX), 0, k,
 			bch2_discard_one_bucket(trans, ca, &iter, &discard_pos_done, &s, false)));
 
+	if (s.need_journal_commit > dev_buckets_available(ca, BCH_WATERMARK_normal))
+		bch2_journal_flush_async(&c->journal, NULL);
+
 	trace_discard_buckets(c, s.seen, s.open, s.need_journal_commit, s.discarded,
 			      bch2_err_str(ret));
 
@@ -2024,7 +2027,7 @@ static void bch2_do_discards_fast_work(struct work_struct *work)
 			break;
 	}
 
-	trace_discard_buckets(c, s.seen, s.open, s.need_journal_commit, s.discarded, bch2_err_str(ret));
+	trace_discard_buckets_fast(c, s.seen, s.open, s.need_journal_commit, s.discarded, bch2_err_str(ret));
 
 	bch2_trans_put(trans);
 	percpu_ref_put(&ca->io_ref);

fs/bcachefs/alloc_foreground.c

@@ -205,8 +205,12 @@ static inline bool may_alloc_bucket(struct bch_fs *c,
 		return false;
 	}
 
-	if (bch2_bucket_needs_journal_commit(&c->buckets_waiting_for_journal,
-			c->journal.flushed_seq_ondisk, bucket.inode, bucket.offset)) {
+	u64 journal_seq_ready =
+		bch2_bucket_journal_seq_ready(&c->buckets_waiting_for_journal,
+					      bucket.inode, bucket.offset);
+	if (journal_seq_ready > c->journal.flushed_seq_ondisk) {
+		if (journal_seq_ready > c->journal.flushing_seq)
+			s->need_journal_commit++;
 		s->skipped_need_journal_commit++;
 		return false;
 	}
@@ -570,7 +574,7 @@ alloc:
 		? bch2_bucket_alloc_freelist(trans, ca, watermark, &s, cl)
 		: bch2_bucket_alloc_early(trans, ca, watermark, &s, cl);
 
-	if (s.skipped_need_journal_commit * 2 > avail)
+	if (s.need_journal_commit * 2 > avail)
 		bch2_journal_flush_async(&c->journal, NULL);
 
 	if (!ob && s.btree_bitmap != BTREE_BITMAP_ANY) {

fs/bcachefs/alloc_types.h

@@ -18,6 +18,7 @@ struct bucket_alloc_state {
 	u64	buckets_seen;
 	u64	skipped_open;
 	u64	skipped_need_journal_commit;
+	u64	need_journal_commit;
 	u64	skipped_nocow;
 	u64	skipped_nouse;
 	u64	skipped_mi_btree_bitmap;

fs/bcachefs/btree_key_cache.c

@@ -748,7 +748,6 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 				rcu_read_unlock();
 				mutex_lock(&bc->table.mutex);
 				mutex_unlock(&bc->table.mutex);
-				rcu_read_lock();
 				continue;
 			}
 			for (i = 0; i < tbl->size; i++)

fs/bcachefs/buckets_waiting_for_journal.c

@@ -22,23 +22,21 @@ static void bucket_table_init(struct buckets_waiting_for_journal_table *t, size_
 	memset(t->d, 0, sizeof(t->d[0]) << t->bits);
 }
 
-bool bch2_bucket_needs_journal_commit(struct buckets_waiting_for_journal *b,
-				      u64 flushed_seq,
-				      unsigned dev, u64 bucket)
+u64 bch2_bucket_journal_seq_ready(struct buckets_waiting_for_journal *b,
+				  unsigned dev, u64 bucket)
 {
 	struct buckets_waiting_for_journal_table *t;
 	u64 dev_bucket = (u64) dev << 56 | bucket;
-	bool ret = false;
-	unsigned i;
+	u64 ret = 0;
 
 	mutex_lock(&b->lock);
 	t = b->t;
 
-	for (i = 0; i < ARRAY_SIZE(t->hash_seeds); i++) {
+	for (unsigned i = 0; i < ARRAY_SIZE(t->hash_seeds); i++) {
 		struct bucket_hashed *h = bucket_hash(t, i, dev_bucket);
 
 		if (h->dev_bucket == dev_bucket) {
-			ret = h->journal_seq > flushed_seq;
+			ret = h->journal_seq;
 			break;
 		}
 	}

fs/bcachefs/buckets_waiting_for_journal.h

@@ -4,8 +4,8 @@
 
 #include "buckets_waiting_for_journal_types.h"
 
-bool bch2_bucket_needs_journal_commit(struct buckets_waiting_for_journal *,
-				      u64, unsigned, u64);
+u64 bch2_bucket_journal_seq_ready(struct buckets_waiting_for_journal *,
+				  unsigned, u64);
 int bch2_set_bucket_needs_journal_commit(struct buckets_waiting_for_journal *,
 					 u64, unsigned, u64, u64);
 

fs/bcachefs/inode.h

@@ -285,12 +285,14 @@ void bch2_inode_opts_get(struct bch_io_opts *, struct bch_fs *,
 			 struct bch_inode_unpacked *);
 int bch2_inum_opts_get(struct btree_trans*, subvol_inum, struct bch_io_opts *);
 
+#include "rebalance.h"
+
 static inline struct bch_extent_rebalance
 bch2_inode_rebalance_opts_get(struct bch_fs *c, struct bch_inode_unpacked *inode)
 {
 	struct bch_io_opts io_opts;
 	bch2_inode_opts_get(&io_opts, c, inode);
-	return io_opts_to_rebalance_opts(&io_opts);
+	return io_opts_to_rebalance_opts(c, &io_opts);
 }
 
 int bch2_inode_rm_snapshot(struct btree_trans *, u64, u32);

fs/bcachefs/journal.c

@@ -319,6 +319,16 @@ void bch2_journal_halt(struct journal *j)
 	spin_unlock(&j->lock);
 }
 
+void bch2_journal_halt_locked(struct journal *j)
+{
+	lockdep_assert_held(&j->lock);
+
+	__journal_entry_close(j, JOURNAL_ENTRY_ERROR_VAL, true);
+	if (!j->err_seq)
+		j->err_seq = journal_cur_seq(j);
+	journal_wake(j);
+}
+
 static bool journal_entry_want_write(struct journal *j)
 {
 	bool ret = !journal_entry_is_open(j) ||
@@ -381,9 +391,12 @@ static int journal_entry_open(struct journal *j)
 	if (nr_unwritten_journal_entries(j) == ARRAY_SIZE(j->buf))
 		return JOURNAL_ERR_max_in_flight;
 
-	if (bch2_fs_fatal_err_on(journal_cur_seq(j) >= JOURNAL_SEQ_MAX,
-				 c, "cannot start: journal seq overflow"))
+	if (journal_cur_seq(j) >= JOURNAL_SEQ_MAX) {
+		bch_err(c, "cannot start: journal seq overflow");
+		if (bch2_fs_emergency_read_only_locked(c))
+			bch_err(c, "fatal error - emergency read only");
 		return JOURNAL_ERR_insufficient_devices; /* -EROFS */
+	}
 
 	BUG_ON(!j->cur_entry_sectors);
 
@@ -783,6 +796,7 @@ recheck_need_open:
 	}
 
 	buf->must_flush = true;
+	j->flushing_seq = max(j->flushing_seq, seq);
 
 	if (parent && !closure_wait(&buf->wait, parent))
 		BUG();

fs/bcachefs/journal.h

@@ -409,6 +409,7 @@ bool bch2_journal_noflush_seq(struct journal *, u64, u64);
 int bch2_journal_meta(struct journal *);
 
 void bch2_journal_halt(struct journal *);
+void bch2_journal_halt_locked(struct journal *);
 
 static inline int bch2_journal_error(struct journal *j)
 {

fs/bcachefs/journal_types.h

@@ -237,6 +237,7 @@ struct journal {
 	/* seq, last_seq from the most recent journal entry successfully written */
 	u64			seq_ondisk;
 	u64			flushed_seq_ondisk;
+	u64			flushing_seq;
 	u64			last_seq_ondisk;
 	u64			err_seq;
 	u64			last_empty_seq;

fs/bcachefs/opts.h

@@ -659,18 +659,4 @@ static inline void bch2_io_opts_fixups(struct bch_io_opts *opts)
 struct bch_io_opts bch2_opts_to_inode_opts(struct bch_opts);
 bool bch2_opt_is_inode_opt(enum bch_opt_id);
 
-/* rebalance opts: */
-
-static inline struct bch_extent_rebalance io_opts_to_rebalance_opts(struct bch_io_opts *opts)
-{
-	return (struct bch_extent_rebalance) {
-		.type = BIT(BCH_EXTENT_ENTRY_rebalance),
-#define x(_name)							\
-		._name = opts->_name,					\
-		._name##_from_inode = opts->_name##_from_inode,
-		BCH_REBALANCE_OPTS()
-#undef x
-	};
-};
-
 #endif /* _BCACHEFS_OPTS_H */

fs/bcachefs/rebalance.c

@@ -121,12 +121,10 @@ u64 bch2_bkey_sectors_need_rebalance(struct bch_fs *c, struct bkey_s_c k)
 		}
 	}
 incompressible:
-	if (opts->background_target &&
-	    bch2_target_accepts_data(c, BCH_DATA_user, opts->background_target)) {
+	if (opts->background_target)
 		bkey_for_each_ptr_decode(k.k, ptrs, p, entry)
 			if (!p.ptr.cached && !bch2_dev_in_target(c, p.ptr.dev, opts->background_target))
 				sectors += p.crc.compressed_size;
-	}
 
 	return sectors;
 }
@@ -140,7 +138,7 @@ static bool bch2_bkey_rebalance_needs_update(struct bch_fs *c, struct bch_io_opt
 	const struct bch_extent_rebalance *old = bch2_bkey_rebalance_opts(k);
 
 	if (k.k->type == KEY_TYPE_reflink_v || bch2_bkey_ptrs_need_rebalance(c, opts, k)) {
-		struct bch_extent_rebalance new = io_opts_to_rebalance_opts(opts);
+		struct bch_extent_rebalance new = io_opts_to_rebalance_opts(c, opts);
 		return old == NULL || memcmp(old, &new, sizeof(new));
 	} else {
 		return old != NULL;
@@ -163,7 +161,7 @@ int bch2_bkey_set_needs_rebalance(struct bch_fs *c, struct bch_io_opts *opts,
 			k.k->u64s += sizeof(*old) / sizeof(u64);
 		}
 
-		*old = io_opts_to_rebalance_opts(opts);
+		*old = io_opts_to_rebalance_opts(c, opts);
 	} else {
 		if (old)
 			extent_entry_drop(k, (union bch_extent_entry *) old);

fs/bcachefs/rebalance.h

@@ -4,8 +4,28 @@
 
 #include "compress.h"
 #include "disk_groups.h"
+#include "opts.h"
 #include "rebalance_types.h"
 
+static inline struct bch_extent_rebalance io_opts_to_rebalance_opts(struct bch_fs *c,
+								    struct bch_io_opts *opts)
+{
+	struct bch_extent_rebalance r = {
+		.type = BIT(BCH_EXTENT_ENTRY_rebalance),
+#define x(_name)							\
+		._name = opts->_name,					\
+		._name##_from_inode = opts->_name##_from_inode,
+		BCH_REBALANCE_OPTS()
+#undef x
+	};
+
+	if (r.background_target &&
+	    !bch2_target_accepts_data(c, BCH_DATA_user, r.background_target))
+		r.background_target = 0;
+
+	return r;
+};
+
 u64 bch2_bkey_sectors_need_rebalance(struct bch_fs *, struct bkey_s_c);
 int bch2_bkey_set_needs_rebalance(struct bch_fs *, struct bch_io_opts *, struct bkey_i *);
 int bch2_get_update_rebalance_opts(struct btree_trans *,

fs/bcachefs/subvolume.c

@@ -428,7 +428,7 @@ static int __bch2_subvolume_delete(struct btree_trans *trans, u32 subvolid)
 		bch2_bkey_get_iter_typed(trans, &snapshot_iter,
 				BTREE_ID_snapshots, POS(0, snapid),
 				0, snapshot);
-	ret = bkey_err(subvol);
+	ret = bkey_err(snapshot);
 	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
 				"missing snapshot %u", snapid);
 	if (ret)
@@ -440,6 +440,11 @@ static int __bch2_subvolume_delete(struct btree_trans *trans, u32 subvolid)
 		bch2_bkey_get_iter_typed(trans, &snapshot_tree_iter,
 				BTREE_ID_snapshot_trees, POS(0, treeid),
 				0, snapshot_tree);
+	ret = bkey_err(snapshot_tree);
+	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
+				"missing snapshot tree %u", treeid);
+	if (ret)
+		goto err;
 
 	if (le32_to_cpu(snapshot_tree.v->master_subvol) == subvolid) {
 		struct bkey_i_snapshot_tree *snapshot_tree_mut =

fs/bcachefs/super.c

@@ -411,6 +411,17 @@ bool bch2_fs_emergency_read_only(struct bch_fs *c)
 	return ret;
 }
 
+bool bch2_fs_emergency_read_only_locked(struct bch_fs *c)
+{
+	bool ret = !test_and_set_bit(BCH_FS_emergency_ro, &c->flags);
+
+	bch2_journal_halt_locked(&c->journal);
+	bch2_fs_read_only_async(c);
+
+	wake_up(&bch2_read_only_wait);
+	return ret;
+}
+
 static int bch2_fs_read_write_late(struct bch_fs *c)
 {
 	int ret;

fs/bcachefs/super.h

@@ -29,6 +29,7 @@ int bch2_dev_resize(struct bch_fs *, struct bch_dev *, u64);
 struct bch_dev *bch2_dev_lookup(struct bch_fs *, const char *);
 
 bool bch2_fs_emergency_read_only(struct bch_fs *);
+bool bch2_fs_emergency_read_only_locked(struct bch_fs *);
 void bch2_fs_read_only(struct bch_fs *);
 
 int bch2_fs_read_write(struct bch_fs *);

fs/bcachefs/trace.h

@@ -727,7 +727,7 @@ DEFINE_EVENT(fs_str, bucket_alloc_fail,
 	TP_ARGS(c, str)
 );
 
-TRACE_EVENT(discard_buckets,
+DECLARE_EVENT_CLASS(discard_buckets_class,
 	TP_PROTO(struct bch_fs *c, u64 seen, u64 open,
 		 u64 need_journal_commit, u64 discarded, const char *err),
 	TP_ARGS(c, seen, open, need_journal_commit, discarded, err),
@@ -759,6 +759,18 @@ TRACE_EVENT(discard_buckets,
 		  __entry->err)
 );
 
+DEFINE_EVENT(discard_buckets_class, discard_buckets,
+	TP_PROTO(struct bch_fs *c, u64 seen, u64 open,
+		 u64 need_journal_commit, u64 discarded, const char *err),
+	TP_ARGS(c, seen, open, need_journal_commit, discarded, err)
+);
+
+DEFINE_EVENT(discard_buckets_class, discard_buckets_fast,
+	TP_PROTO(struct bch_fs *c, u64 seen, u64 open,
+		 u64 need_journal_commit, u64 discarded, const char *err),
+	TP_ARGS(c, seen, open, need_journal_commit, discarded, err)
+);
+
 TRACE_EVENT(bucket_invalidate,
 	TP_PROTO(struct bch_fs *c, unsigned dev, u64 bucket, u32 sectors),
 	TP_ARGS(c, dev, bucket, sectors),