KMSAN: uninit-value in bch2

KMSAN: uninit-value in bch2_copygc (2)

Status: upstream: reported on 2025/03/31 14:06
Subsystems: bcachefs
[Documentation on labels]
Reported-by: syzbot+cebfe3f22eeaff4ddd7c@syzkaller.appspotmail.com
Fix commit: 9ea24b287b3b bcachefs: Eliminate padding in move_bucket_key
Patched on: [ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-leak ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-selinux-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci2-upstream-kcsan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu2-arm32 ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-gce-arm64 ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-usb]
First crash: 5d17h, last: 5d17h

▶ ▼ Discussions (1)

Title	Replies (including bot)	Last reply
[syzbot] [bcachefs?] KMSAN: uninit-value in bch2_copygc (2)	0 (2)	2025/04/01 04:10

▶ ▼ Similar bugs (1)

Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KMSAN: uninit-value in bch2_copygc bcachefs	C			88	80d	144d	0/28	auto-obsoleted due to no activity on 2025/03/22 22:59

Sample crash report:

=====================================================
BUG: KMSAN: uninit-value in rht_ptr_rcu include/linux/rhashtable.h:376 [inline]
BUG: KMSAN: uninit-value in __rhashtable_lookup include/linux/rhashtable.h:607 [inline]
BUG: KMSAN: uninit-value in rhashtable_lookup include/linux/rhashtable.h:646 [inline]
BUG: KMSAN: uninit-value in rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
BUG: KMSAN: uninit-value in bucket_in_flight fs/bcachefs/movinggc.c:143 [inline]
BUG: KMSAN: uninit-value in bch2_copygc_get_buckets fs/bcachefs/movinggc.c:169 [inline]
BUG: KMSAN: uninit-value in bch2_copygc+0x1d5c/0x5e00 fs/bcachefs/movinggc.c:221
 rht_ptr_rcu include/linux/rhashtable.h:376 [inline]
 __rhashtable_lookup include/linux/rhashtable.h:607 [inline]
 rhashtable_lookup include/linux/rhashtable.h:646 [inline]
 rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
 bucket_in_flight fs/bcachefs/movinggc.c:143 [inline]
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:169 [inline]
 bch2_copygc+0x1d5c/0x5e00 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x7d2/0xf80 fs/bcachefs/movinggc.c:383
 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 b214.i created at:
 bucket_in_flight fs/bcachefs/movinggc.c:-1 [inline]
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:169 [inline]
 bch2_copygc+0x159e/0x5e00 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x7d2/0xf80 fs/bcachefs/movinggc.c:383

CPU: 1 UID: 0 PID: 5998 Comm: bch-copygc/loop Not tainted 6.14.0-syzkaller-03576-g1e1ba8d23dae #0 PREEMPT(undef) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
=====================================================
Kernel panic - not syncing: kmsan.panic set ...
CPU: 1 UID: 0 PID: 5998 Comm: bch-copygc/loop Tainted: G    B              6.14.0-syzkaller-03576-g1e1ba8d23dae #0 PREEMPT(undef) 
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x216/0x2d0 lib/dump_stack.c:120
 dump_stack+0x1e/0x24 lib/dump_stack.c:129
 panic+0x4e5/0xcf0 kernel/panic.c:354
 kmsan_report+0x2ca/0x2d0 mm/kmsan/report.c:218
 __msan_warning+0x95/0x120 mm/kmsan/instrumentation.c:318
 rht_ptr_rcu include/linux/rhashtable.h:376 [inline]
 __rhashtable_lookup include/linux/rhashtable.h:607 [inline]
 rhashtable_lookup include/linux/rhashtable.h:646 [inline]
 rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
 bucket_in_flight fs/bcachefs/movinggc.c:143 [inline]
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:169 [inline]
 bch2_copygc+0x1d5c/0x5e00 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x7d2/0xf80 fs/bcachefs/movinggc.c:383
 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
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (1):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Assets (help?)	Manager	Title
2025/03/27 14:01	upstream	1e1ba8d23dae	20510e88	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci-upstream-kmsan-gce-root	KMSAN: uninit-value in bch2_copygc

* ~~Struck through~~ repros no longer work on HEAD.