Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_copygc

[syzbot <syzbot+8689d10f1894eedf774d@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: uninit-value in bch2_copygc

=====================================================
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:144 [inline]
BUG: KMSAN: uninit-value in bch2_copygc_get_buckets fs/bcachefs/movinggc.c:170 [inline]
BUG: KMSAN: uninit-value in bch2_copygc+0x1d3f/0x58f0 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:144 [inline]
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:170 [inline]
 bch2_copygc+0x1d3f/0x58f0 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x835/0xfe0 fs/bcachefs/movinggc.c:383
 kthread+0x3e2/0x540 kernel/kthread.c:389
 ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Local variable b205.i created at:
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:170 [inline]
 bch2_copygc+0x15b3/0x58f0 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x835/0xfe0 fs/bcachefs/movinggc.c:383

CPU: 0 UID: 0 PID: 6674 Comm: bch-copygc/loop Not tainted 6.12.0-rc7-syzkaller-g2d5404caa8c7-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
=====================================================
Kernel panic - not syncing: kmsan.panic set ...
CPU: 0 UID: 0 PID: 6674 Comm: bch-copygc/loop Tainted: G    B              6.12.0-rc7-syzkaller-g2d5404caa8c7-dirty #0
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x216/0x2d0 lib/dump_stack.c:120
 dump_stack+0x1e/0x30 lib/dump_stack.c:129
 panic+0x4e2/0xcf0 kernel/panic.c:354
 kmsan_report+0x2c7/0x2d0 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:144 [inline]
 bch2_copygc_get_buckets fs/bcachefs/movinggc.c:170 [inline]
 bch2_copygc+0x1d3f/0x58f0 fs/bcachefs/movinggc.c:221
 bch2_copygc_thread+0x835/0xfe0 fs/bcachefs/movinggc.c:383
 kthread+0x3e2/0x540 kernel/kthread.c:389
 ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Kernel Offset: disabled


Tested on:

commit:         2d5404ca Linux 6.12-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13f8535f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dcca673786a14715
dashboard link: https://syzkaller.appspot.com/bug?extid=8689d10f1894eedf774d
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1008535f980000