[syzbot] [bcachefs?] KMSAN: uninit-value in bch2_copygc (2)

[syzbot] [bcachefs?] KMSAN: uninit-value in bch2_copygc (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1e1ba8d23dae Merge tag 'timers-clocksource-2025-03-26' of ..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15a8ede4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=887673359f1a92bf
dashboard link: https://syzkaller.appspot.com/bug?extid=cebfe3f22eeaff4ddd7c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/97b3a10186d9/disk-1e1ba8d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/de4a9446d205/vmlinux-1e1ba8d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/529352453703/bzImage-1e1ba8d2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cebfe3f22eeaff4ddd7c@syzkaller.appspotmail.com

=====================================================
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..


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Subject: 
Author: kent.overstreet@linux.dev

#syz fix bcachefs: Eliminate padding in move_bucket_key