bcachefs: Fix scheduling while atomic from logging changes

Two fixes from the recent logging changes:

bch2_inconsistent(), bch2_fs_inconsistent() be called from interrupt
context, or with rcu_read_lock() held.

The one syzbot found is in
  bch2_bkey_pick_read_device
  bch2_dev_rcu
  bch2_fs_inconsistent

We're starting to switch to lift the printbufs up to higher levels so we
can emit better log messages and print them all in one go (avoid
garbling), so that conversion will help with spotting these in the
future; when we declare a printbuf it must be flagged if we're in an
atomic context.

Secondly, in btree_node_write_endio:

00085 BUG: sleeping function called from invalid context at include/linux/sched/mm.h:321
00085 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 618, name: bch-reclaim/fa6
00085 preempt_count: 10001, expected: 0
00085 RCU nest depth: 0, expected: 0
00085 4 locks held by bch-reclaim/fa6/618:
00085  #0: ffffff80d7ccad68 (&j->reclaim_lock){+.+.}-{4:4}, at: bch2_journal_reclaim_thread+0x84/0x198
00085  CachyOS#1: ffffff80d7c84218 (&c->btree_trans_barrier){.+.+}-{0:0}, at: __bch2_trans_get+0x1c0/0x440
00085  CachyOS#2: ffffff80cd3f8140 (bcachefs_btree){+.+.}-{0:0}, at: __bch2_trans_get+0x22c/0x440
00085  CachyOS#3: ffffff80c3823c20 (&vblk->vqs[i].lock){-.-.}-{3:3}, at: virtblk_done+0x58/0x130
00085 irq event stamp: 328
00085 hardirqs last  enabled at (327): [<ffffffc080073a14>] finish_task_switch.isra.0+0xbc/0x2a0
00085 hardirqs last disabled at (328): [<ffffffc080971a10>] el1_interrupt+0x20/0x60
00085 softirqs last  enabled at (0): [<ffffffc08002f920>] copy_process+0x7c8/0x2118
00085 softirqs last disabled at (0): [<0000000000000000>] 0x0
00085 Preemption disabled at:
00085 [<ffffffc08003ada0>] irq_enter_rcu+0x18/0x90
00085 CPU: 8 UID: 0 PID: 618 Comm: bch-reclaim/fa6 Not tainted 6.14.0-rc6-ktest-g04630bde23e8 #18798
00085 Hardware name: linux,dummy-virt (DT)
00085 Call trace:
00085  show_stack+0x1c/0x30 (C)
00085  dump_stack_lvl+0x84/0xc0
00085  dump_stack+0x14/0x20
00085  __might_resched+0x180/0x288
00085  __might_sleep+0x4c/0x88
00085  __kmalloc_node_track_caller_noprof+0x34c/0x3e0
00085  krealloc_noprof+0x1a0/0x2d8
00085  bch2_printbuf_make_room+0x9c/0x120
00085  bch2_prt_printf+0x60/0x1b8
00085  btree_node_write_endio+0x1b0/0x2d8
00085  bio_endio+0x138/0x1f0
00085  btree_node_write_endio+0xe8/0x2d8
00085  bio_endio+0x138/0x1f0
00085  blk_update_request+0x220/0x4c0
00085  blk_mq_end_request+0x28/0x148
00085  virtblk_request_done+0x64/0xe8
00085  blk_mq_complete_request+0x34/0x40
00085  virtblk_done+0x78/0x130
00085  vring_interrupt+0x6c/0xb0
00085  __handle_irq_event_percpu+0x8c/0x2e0
00085  handle_irq_event+0x50/0xb0
00085  handle_fasteoi_irq+0xc4/0x250
00085  handle_irq_desc+0x44/0x60
00085  generic_handle_domain_irq+0x20/0x30
00085  gic_handle_irq+0x54/0xc8
00085  call_on_irq_stack+0x24/0x40

Reported-by: syzbot+c82cd2906e2f192410bb@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

Diff for: fs/bcachefs/btree_io.c

@@ -2146,6 +2146,7 @@ static void btree_node_write_endio(struct bio *bio)
 
 	if (ca && bio->bi_status) {
 		struct printbuf buf = PRINTBUF;
+		buf.atomic++;
 		prt_printf(&buf, "btree write error: %s\n  ",
 			   bch2_blk_status_to_str(bio->bi_status));
 		bch2_btree_pos_to_text(&buf, c, b);

Diff for: fs/bcachefs/error.c

@@ -45,6 +45,8 @@ bool __bch2_inconsistent_error(struct bch_fs *c, struct printbuf *out)
 bool bch2_inconsistent_error(struct bch_fs *c)
 {
 	struct printbuf buf = PRINTBUF;
+	buf.atomic++;
+
 	printbuf_indent_add_nextline(&buf, 2);
 
 	bool ret = __bch2_inconsistent_error(c, &buf);
@@ -59,6 +61,7 @@ static bool bch2_fs_trans_inconsistent(struct bch_fs *c, struct btree_trans *tra
 				       const char *fmt, va_list args)
 {
 	struct printbuf buf = PRINTBUF;
+	buf.atomic++;
 
 	bch2_log_msg_start(c, &buf);