[syzbot] [btrfs?] KMSAN: uninit-value in bcmp (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    610a9b8f49fb Linux 6.7-rc8
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=110b4555e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e51fe20c3e51ba7f
dashboard link: https://syzkaller.appspot.com/bug?extid=3ce5dea5b1539ff36769
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: i386

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/daced691c987/disk-610a9b8f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5e37367a7d1e/vmlinux-610a9b8f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/013b65c960ab/bzImage-610a9b8f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ce5dea5b1539ff36769@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in memcmp lib/string.c:681 [inline]
BUG: KMSAN: uninit-value in bcmp+0xc3/0x1c0 lib/string.c:713
 memcmp lib/string.c:681 [inline]
 bcmp+0xc3/0x1c0 lib/string.c:713
 sample_repeated_patterns fs/btrfs/compression.c:1298 [inline]
 btrfs_compress_heuristic+0x926/0x31f0 fs/btrfs/compression.c:1380
 inode_need_compress fs/btrfs/inode.c:804 [inline]
 btrfs_run_delalloc_range+0x156c/0x16c0 fs/btrfs/inode.c:2272
 writepage_delalloc+0x244/0x6b0 fs/btrfs/extent_io.c:1189
 __extent_writepage fs/btrfs/extent_io.c:1440 [inline]
 extent_write_cache_pages fs/btrfs/extent_io.c:2108 [inline]
 extent_writepages+0x1d22/0x3f20 fs/btrfs/extent_io.c:2230
 btrfs_writepages+0x35/0x40 fs/btrfs/inode.c:7836
 do_writepages+0x426/0x870 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:387
 start_delalloc_inodes+0x91d/0x1560 fs/btrfs/inode.c:9284
 btrfs_start_delalloc_roots+0x874/0xe80 fs/btrfs/inode.c:9361
 shrink_delalloc fs/btrfs/space-info.c:649 [inline]
 flush_space+0xbd4/0x16c0 fs/btrfs/space-info.c:759
 btrfs_async_reclaim_metadata_space+0x76d/0x9c0 fs/btrfs/space-info.c:1089
 process_one_work kernel/workqueue.c:2627 [inline]
 process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700
 worker_thread+0xf45/0x1490 kernel/workqueue.c:2781
 kthread+0x3ed/0x540 kernel/kthread.c:388
 ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

Uninit was stored to memory at:
 heuristic_collect_sample fs/btrfs/compression.c:1338 [inline]
 btrfs_compress_heuristic+0x303/0x31f0 fs/btrfs/compression.c:1378
 inode_need_compress fs/btrfs/inode.c:804 [inline]
 btrfs_run_delalloc_range+0x156c/0x16c0 fs/btrfs/inode.c:2272
 writepage_delalloc+0x244/0x6b0 fs/btrfs/extent_io.c:1189
 __extent_writepage fs/btrfs/extent_io.c:1440 [inline]
 extent_write_cache_pages fs/btrfs/extent_io.c:2108 [inline]
 extent_writepages+0x1d22/0x3f20 fs/btrfs/extent_io.c:2230
 btrfs_writepages+0x35/0x40 fs/btrfs/inode.c:7836
 do_writepages+0x426/0x870 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:387
 start_delalloc_inodes+0x91d/0x1560 fs/btrfs/inode.c:9284
 btrfs_start_delalloc_roots+0x874/0xe80 fs/btrfs/inode.c:9361
 shrink_delalloc fs/btrfs/space-info.c:649 [inline]
 flush_space+0xbd4/0x16c0 fs/btrfs/space-info.c:759
 btrfs_async_reclaim_metadata_space+0x76d/0x9c0 fs/btrfs/space-info.c:1089
 process_one_work kernel/workqueue.c:2627 [inline]
 process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700
 worker_thread+0xf45/0x1490 kernel/workqueue.c:2781
 kthread+0x3ed/0x540 kernel/kthread.c:388
 ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

Uninit was created at:
 __alloc_pages+0x9a4/0xe00 mm/page_alloc.c:4591
 alloc_pages_mpol+0x62b/0x9d0 mm/mempolicy.c:2133
 alloc_pages mm/mempolicy.c:2204 [inline]
 folio_alloc+0x1da/0x380 mm/mempolicy.c:2211
 filemap_alloc_folio+0xa5/0x430 mm/filemap.c:974
 __filemap_get_folio+0xa5a/0x1760 mm/filemap.c:1918
 pagecache_get_page+0x4a/0x1a0 mm/folio-compat.c:99
 prepare_pages+0x1f2/0x1050 fs/btrfs/file.c:922
 btrfs_buffered_write+0xe48/0x2be0 fs/btrfs/file.c:1316
 btrfs_do_write_iter+0x370/0x2300 fs/btrfs/file.c:1687
 btrfs_file_write_iter+0x38/0x40 fs/btrfs/file.c:1704
 __kernel_write_iter+0x329/0x930 fs/read_write.c:517
 dump_emit_page fs/coredump.c:888 [inline]
 dump_user_range+0x593/0xcd0 fs/coredump.c:915
 elf_core_dump+0x59e8/0x5c60 fs/binfmt_elf.c:2077
 do_coredump+0x32c9/0x4920 fs/coredump.c:764
 get_signal+0x2185/0x2d10 kernel/signal.c:2890
 arch_do_signal_or_restart+0x53/0xca0 arch/x86/kernel/signal.c:309
 exit_to_user_mode_loop+0xe8/0x320 kernel/entry/common.c:168
 exit_to_user_mode_prepare+0x163/0x220 kernel/entry/common.c:204
 irqentry_exit_to_user_mode+0xd/0x30 kernel/entry/common.c:309
 irqentry_exit+0x16/0x40 kernel/entry/common.c:412
 exc_page_fault+0x246/0x6f0 arch/x86/mm/fault.c:1564
 asm_exc_page_fault+0x2b/0x30 arch/x86/include/asm/idtentry.h:570

CPU: 1 PID: 56 Comm: kworker/u4:4 Not tainted 6.7.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Workqueue: events_unbound btrfs_async_reclaim_metadata_space
=====================================================


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