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Message-ID: <CACzwLxgJb=xUCO+TFN_Y6SZ6YxoRn=pg0yfif3+GuHK8kL3x0Q@mail.gmail.com>
Date: Mon, 14 Oct 2024 11:40:05 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: syzbot <syzbot+b79be83906cd9bab16ff@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
syzkaller-bugs@...glegroups.com, willy@...radead.org
Subject: Re: [syzbot] [fs?] [mm?] KCSAN: data-race in xas_create / xas_find (8)
On Mon, Oct 14, 2024 at 11:08 AM syzbot
<syzbot+b79be83906cd9bab16ff@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 2f91ff27b0ee Merge tag 'sound-6.12-rc2' of git://git.kerne..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=155c879f980000
> kernel config: https://syzkaller.appspot.com/x/.config?x=95098faba89c70c9
> dashboard link: https://syzkaller.appspot.com/bug?extid=b79be83906cd9bab16ff
> 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/14933c4ac457/disk-2f91ff27.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6725831fc1a1/vmlinux-2f91ff27.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/98d64e038e72/bzImage-2f91ff27.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b79be83906cd9bab16ff@...kaller.appspotmail.com
>
> loop4: detected capacity change from 0 to 4096
> EXT4-fs: Ignoring removed nobh option
> EXT4-fs: Ignoring removed i_version option
> ==================================================================
> BUG: KCSAN: data-race in xas_create / xas_find
>
> write to 0xffff888106819919 of 1 bytes by task 3435 on cpu 0:
> xas_expand lib/xarray.c:613 [inline]
> xas_create+0x666/0xbd0 lib/xarray.c:654
> xas_store+0x6f/0xc90 lib/xarray.c:788
AFAIU, xas_store() itself, doesn't have a locking mechanism,
but is locked in xa_* functions. Example:
void *xa_store_range(...)
{
XA_STATE(xas, xa, 0);
...
do {
xas_lock(&xas);
if (entry) {
...
xas_create(&xas, true);
}
...
unlock:
xas_unlock(&xas);
}
Same thing is for the another racing xas_find() function:
void *xa_find(...)
{
XA_STATE(xas, xa, *indexp);
void *entry;
rcu_read_lock();
do {
if (...)
entry = xas_find_marked(&xas, max, filter);
else
entry = xas_find(&xas, max);
...
rcu_read_unlock();
}
In this KCSAN report, xas_create() and xas_find() are racing for `offset` field.
> __filemap_add_folio+0x3cc/0x6f0 mm/filemap.c:916
> filemap_add_folio+0x9c/0x1b0 mm/filemap.c:972
> page_cache_ra_unbounded+0x175/0x310 mm/readahead.c:268
> do_page_cache_ra mm/readahead.c:320 [inline]
> force_page_cache_ra mm/readahead.c:349 [inline]
> page_cache_sync_ra+0x252/0x670 mm/readahead.c:562
> page_cache_sync_readahead include/linux/pagemap.h:1394 [inline]
> filemap_get_pages+0x2c1/0x10e0 mm/filemap.c:2547
> filemap_read+0x216/0x680 mm/filemap.c:2645
> blkdev_read_iter+0x20e/0x2c0 block/fops.c:765
> new_sync_read fs/read_write.c:488 [inline]
> vfs_read+0x5f6/0x720 fs/read_write.c:569
> ksys_read+0xeb/0x1b0 fs/read_write.c:712
> __do_sys_read fs/read_write.c:722 [inline]
> __se_sys_read fs/read_write.c:720 [inline]
> __x64_sys_read+0x42/0x50 fs/read_write.c:720
> x64_sys_call+0x27d3/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:1
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> read to 0xffff888106819919 of 1 bytes by task 9109 on cpu 1:
> xas_find+0x372/0x3f0 lib/xarray.c:1278
> find_get_entry+0x66/0x390 mm/filemap.c:1992
> find_get_entries+0xa4/0x220 mm/filemap.c:2047
> truncate_inode_pages_range+0x4ac/0x6b0 mm/truncate.c:378
> truncate_inode_pages+0x24/0x30 mm/truncate.c:423
> kill_bdev block/bdev.c:91 [inline]
> set_blocksize+0x258/0x270 block/bdev.c:173
> sb_set_blocksize block/bdev.c:182 [inline]
> sb_min_blocksize+0x63/0xe0 block/bdev.c:198
> ext4_load_super fs/ext4/super.c:4992 [inline]
> __ext4_fill_super fs/ext4/super.c:5213 [inline]
> ext4_fill_super+0x38b/0x3a10 fs/ext4/super.c:5686
> get_tree_bdev+0x256/0x2e0 fs/super.c:1635
> ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5718
> vfs_get_tree+0x56/0x1e0 fs/super.c:1800
> do_new_mount+0x227/0x690 fs/namespace.c:3507
> path_mount+0x49b/0xb30 fs/namespace.c:3834
> do_mount fs/namespace.c:3847 [inline]
> __do_sys_mount fs/namespace.c:4055 [inline]
> __se_sys_mount+0x27c/0x2d0 fs/namespace.c:4032
> __x64_sys_mount+0x67/0x80 fs/namespace.c:4032
> x64_sys_call+0x203e/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:166
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> value changed: 0x0e -> 0x00
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 UID: 0 PID: 9109 Comm: syz.4.1794 Not tainted 6.12.0-rc1-syzkaller-00257-g2f91ff27b0ee #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> ==================================================================
> EXT4-fs (loop4): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
> EXT4-fs (loop4): unmounting filesystem 00000000-0000-0000-0000-000000000000.
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup
>
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