Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_bucket_alloc_trans

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    2df0c02dab82 x86 boot build: make git ignore stale 'tools'..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=135c6a4c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=afd286fb06ecc311
dashboard link: https://syzkaller.appspot.com/bug?extid=c761143a86b1640bc485
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10355804580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16c86198580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4df46ef3da39/disk-2df0c02d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7585a408245b/vmlinux-2df0c02d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2f16d3f20d29/bzImage-2df0c02d.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/e2708f9fb487/mount_5.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c761143a86b1640bc485@xxxxxxxxxxxxxxxxxxxxxxxxx

  fragmentation     0
  bp_start          8
  incorrectly set at freespace:0:31:0 (free 0, genbits 0 should be 0), fixing
=====================================================
BUG: KMSAN: uninit-value in try_alloc_bucket fs/bcachefs/alloc_foreground.c:297 [inline]
BUG: KMSAN: uninit-value in bch2_bucket_alloc_freelist fs/bcachefs/alloc_foreground.c:442 [inline]
BUG: KMSAN: uninit-value in bch2_bucket_alloc_trans+0x2191/0x3280 fs/bcachefs/alloc_foreground.c:574
 try_alloc_bucket fs/bcachefs/alloc_foreground.c:297 [inline]
 bch2_bucket_alloc_freelist fs/bcachefs/alloc_foreground.c:442 [inline]
 bch2_bucket_alloc_trans+0x2191/0x3280 fs/bcachefs/alloc_foreground.c:574
 bch2_bucket_alloc_set_trans+0x935/0x1620 fs/bcachefs/alloc_foreground.c:730
 __open_bucket_add_buckets+0x1e98/0x3130 fs/bcachefs/alloc_foreground.c:973
 open_bucket_add_buckets+0x32b/0x530 fs/bcachefs/alloc_foreground.c:1017
 bch2_alloc_sectors_start_trans+0x1839/0x32d0
 __bch2_btree_node_alloc fs/bcachefs/btree_update_interior.c:322 [inline]
 bch2_btree_reserve_get+0x9eb/0x22b0 fs/bcachefs/btree_update_interior.c:532
 bch2_btree_update_start+0x22b8/0x2ec0 fs/bcachefs/btree_update_interior.c:1232
 bch2_btree_node_rewrite+0x1da/0x1af0 fs/bcachefs/btree_update_interior.c:2144
 async_btree_node_rewrite_trans fs/bcachefs/btree_update_interior.c:2217 [inline]
 async_btree_node_rewrite_work+0x74c/0x1aa0 fs/bcachefs/btree_update_interior.c:2253
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xc1d/0x1e80 kernel/workqueue.c:3319
 worker_thread+0xea7/0x14f0 kernel/workqueue.c:3400
 kthread+0x6b9/0xef0 kernel/kthread.c:464
 ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Local variable gen.i.i created at:
 bch2_bucket_alloc_freelist fs/bcachefs/alloc_foreground.c:442 [inline]
 bch2_bucket_alloc_trans+0x1fb2/0x3280 fs/bcachefs/alloc_foreground.c:574
 bch2_bucket_alloc_set_trans+0x935/0x1620 fs/bcachefs/alloc_foreground.c:730

CPU: 1 UID: 0 PID: 4283 Comm: kworker/u8:21 Not tainted 6.14.0-syzkaller-01103-g2df0c02dab82 #0 PREEMPT(undef) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: btree_node_rewrite async_btree_node_rewrite_work
=====================================================


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