[syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    41cd3fd15263 Merge tag 'pci-v6.17-fixes-2' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11ef37a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e1e1566c7726877e
dashboard link: https://syzkaller.appspot.com/bug?extid=a725ab460fc1def9896f
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17a857a2580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14c916f0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bc397a2f4204/disk-41cd3fd1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5291086f4669/vmlinux-41cd3fd1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1099e6ad84b5/bzImage-41cd3fd1.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/c1980868ad6b/mount_0.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=10e28fa2580000)

The issue was bisected to:

commit d2d6422f8bd17c6bb205133e290625a564194496
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Fri Sep 6 10:59:04 2024 +0000

    x86: Allow to enable PREEMPT_RT.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16cf8fa2580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=15cf8fa2580000
console output: https://syzkaller.appspot.com/x/log.txt?x=11cf8fa2580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a725ab460fc1def9896f@syzkaller.appspotmail.com
Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.")

exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
------------[ cut here ]------------
rtmutex deadlock detected
WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 rt_mutex_handle_deadlock kernel/locking/rtmutex.c:1674 [inline]
WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock kernel/locking/rtmutex.c:1734 [inline]
WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock_locked+0xed2/0x25e0 kernel/locking/rtmutex.c:1760
Modules linked in:
CPU: 0 UID: 0 PID: 6000 Comm: syz.0.17 Tainted: G        W           syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:rt_mutex_handle_deadlock kernel/locking/rtmutex.c:1674 [inline]
RIP: 0010:__rt_mutex_slowlock kernel/locking/rtmutex.c:1734 [inline]
RIP: 0010:__rt_mutex_slowlock_locked+0xed2/0x25e0 kernel/locking/rtmutex.c:1760
Code: 7c 24 20 dd 4c 8b b4 24 98 00 00 00 0f 85 fd 0a 00 00 48 8b 7c 24 10 e8 2c ee 5d 09 90 48 c7 c7 00 ed 0a 8b e8 df 89 e7 ff 90 <0f> 0b 90 90 48 8b 9c 24 80 00 00 00 43 80 3c 3e 00 74 08 4c 89 e7
RSP: 0018:ffffc900048df840 EFLAGS: 00010246
RAX: e12880a9366a4400 RBX: ffff8880324663e0 RCX: ffff888032465940
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900048dfa30 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed1017104863 R12: ffff888032467060
R13: ffff888032465958 R14: 1ffff1100648ce0c R15: dffffc0000000000
FS:  0000555557981500(0000) GS:ffff8881268c5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000035be0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 rt_mutex_slowlock+0xb5/0x160 kernel/locking/rtmutex.c:1800
 __rt_mutex_lock kernel/locking/rtmutex.c:1815 [inline]
 rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244
 inode_lock_nested include/linux/fs.h:914 [inline]
 vfs_rename+0x68f/0xf00 fs/namei.c:5092
 do_renameat2+0x6ce/0xa80 fs/namei.c:5278
 __do_sys_renameat2 fs/namei.c:5312 [inline]
 __se_sys_renameat2 fs/namei.c:5309 [inline]
 __x64_sys_renameat2+0xce/0xe0 fs/namei.c:5309
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc9cdd7ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe70cc6ad8 EFLAGS: 00000246 ORIG_RAX: 000000000000013c
RAX: ffffffffffffffda RBX: 00007fc9cdfa5fa0 RCX: 00007fc9cdd7ebe9
RDX: 0000000000000004 RSI: 00002000000001c0 RDI: 0000000000000004
RBP: 00007fc9cde01e19 R08: 0000000000000004 R09: 0000000000000000
R10: 0000200000000140 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc9cdfa5fa0 R14: 00007fc9cdfa5fa0 R15: 0000000000000005
 </TASK>


---
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Re: [syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[Sebastian Andrzej Siewior]

On 2025-08-21 07:08:32 [-0700], syzbot wrote:
> dashboard link: https://syzkaller.appspot.com/bug?extid=a725ab460fc1def9896f
…
> The issue was bisected to:
> 
> commit d2d6422f8bd17c6bb205133e290625a564194496
> Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Date:   Fri Sep 6 10:59:04 2024 +0000
> 
>     x86: Allow to enable PREEMPT_RT.
> 
…
> exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
> exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
> ------------[ cut here ]------------
> rtmutex deadlock detected
> WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 rt_mutex_handle_deadlock kernel/locking/rtmutex.c:1674 [inline]
> WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock kernel/locking/rtmutex.c:1734 [inline]
> WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock_locked+0xed2/0x25e0 kernel/locking/rtmutex.c:1760

RT detected a deadlock and complained. The same testcase on !RT results
in:

| [   15.363878] loop0: detected capacity change from 0 to 256
| [   15.367981] exFAT-fs (loop0): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
| [   15.373808] exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
| [   15.380396] exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
| [   62.668182] INFO: task exfat-repro:2155 blocked for more than 30 seconds.
| [   62.669405]       Not tainted 6.17.0-rc2+ #10
| [   62.670181] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
| [   62.671612] task:exfat-repro     state:D stack:0     pid:2155  tgid:2155  ppid:1      task_flags:0x400140 flags:0x00004006
| [   62.673557] Call Trace:
| [   62.674008]  <TASK>
| [   62.674400]  __schedule+0x4ef/0xbb0
| [   62.675069]  schedule+0x22/0xd0
| [   62.675656]  schedule_preempt_disabled+0x10/0x20
| [   62.676495]  rwsem_down_write_slowpath+0x1e2/0x6c0
| [   62.679028]  down_write+0x66/0x70
| [   62.679645]  vfs_rename+0x5c6/0xc30
| [   62.681734]  do_renameat2+0x3c4/0x570
| [   62.682395]  __x64_sys_renameat2+0x7b/0xc0
| [   62.683187]  do_syscall_64+0x7f/0x290
| [   62.695576]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

After ctrl+c that testcase terminates but one thread remains in D state.
This is from 
|         lock_new_subdir = new_dir != old_dir || !(flags & RENAME_EXCHANGE);
|         if (is_dir) {
|                 if (lock_old_subdir)
|                         inode_lock_nested(source, I_MUTEX_CHILD);
                          ^^^
| 5 locks held by exfat-repro/2156:
|  #0: ffff888113b69400 (sb_writers#11){.+.+}-{0:0}, at: do_renameat2+0x1c8/0x580
|  #1: ffff888113b69710 (&type->s_vfs_rename_key){+.+.}-{4:4}, at: do_renameat2+0x24d/0x580
|  #2: ffff88810fb79b88 (&sb->s_type->i_mutex_key#16/1){+.+.}-{4:4}, at: lock_two_directories+0x6c/0x110
|  #3: ffff88810fb7a1c0 (&sb->s_type->i_mutex_key#17/5){+.+.}-{4:4}, at: lock_two_directories+0x82/0x110
|  #4: ffffffff82f618a0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184

#2 and #3 are from the "(r == p1)" case. The lock it appears to acquire
is #2.
Could an exfat take a look, please?

Sebastian

Re: [syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[Namjae Jeon]

On Sat, Aug 23, 2025 at 1:20 AM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> On 2025-08-21 07:08:32 [-0700], syzbot wrote:
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a725ab460fc1def9896f
> …
> > The issue was bisected to:
> >
> > commit d2d6422f8bd17c6bb205133e290625a564194496
> > Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Date:   Fri Sep 6 10:59:04 2024 +0000
> >
> >     x86: Allow to enable PREEMPT_RT.
> >
> …
> > exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
> > exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
> > ------------[ cut here ]------------
> > rtmutex deadlock detected
> > WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 rt_mutex_handle_deadlock kernel/locking/rtmutex.c:1674 [inline]
> > WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock kernel/locking/rtmutex.c:1734 [inline]
> > WARNING: CPU: 0 PID: 6000 at kernel/locking/rtmutex.c:1674 __rt_mutex_slowlock_locked+0xed2/0x25e0 kernel/locking/rtmutex.c:1760
>
> RT detected a deadlock and complained. The same testcase on !RT results
> in:
>
> | [   15.363878] loop0: detected capacity change from 0 to 256
> | [   15.367981] exFAT-fs (loop0): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
> | [   15.373808] exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
> | [   15.380396] exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
> | [   62.668182] INFO: task exfat-repro:2155 blocked for more than 30 seconds.
> | [   62.669405]       Not tainted 6.17.0-rc2+ #10
> | [   62.670181] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> | [   62.671612] task:exfat-repro     state:D stack:0     pid:2155  tgid:2155  ppid:1      task_flags:0x400140 flags:0x00004006
> | [   62.673557] Call Trace:
> | [   62.674008]  <TASK>
> | [   62.674400]  __schedule+0x4ef/0xbb0
> | [   62.675069]  schedule+0x22/0xd0
> | [   62.675656]  schedule_preempt_disabled+0x10/0x20
> | [   62.676495]  rwsem_down_write_slowpath+0x1e2/0x6c0
> | [   62.679028]  down_write+0x66/0x70
> | [   62.679645]  vfs_rename+0x5c6/0xc30
> | [   62.681734]  do_renameat2+0x3c4/0x570
> | [   62.682395]  __x64_sys_renameat2+0x7b/0xc0
> | [   62.683187]  do_syscall_64+0x7f/0x290
> | [   62.695576]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> After ctrl+c that testcase terminates but one thread remains in D state.
> This is from
> |         lock_new_subdir = new_dir != old_dir || !(flags & RENAME_EXCHANGE);
> |         if (is_dir) {
> |                 if (lock_old_subdir)
> |                         inode_lock_nested(source, I_MUTEX_CHILD);
>                           ^^^
> | 5 locks held by exfat-repro/2156:
> |  #0: ffff888113b69400 (sb_writers#11){.+.+}-{0:0}, at: do_renameat2+0x1c8/0x580
> |  #1: ffff888113b69710 (&type->s_vfs_rename_key){+.+.}-{4:4}, at: do_renameat2+0x24d/0x580
> |  #2: ffff88810fb79b88 (&sb->s_type->i_mutex_key#16/1){+.+.}-{4:4}, at: lock_two_directories+0x6c/0x110
> |  #3: ffff88810fb7a1c0 (&sb->s_type->i_mutex_key#17/5){+.+.}-{4:4}, at: lock_two_directories+0x82/0x110
> |  #4: ffffffff82f618a0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184
>
> #2 and #3 are from the "(r == p1)" case. The lock it appears to acquire
> is #2.
> Could an exfat take a look, please?
I will take a look.
Thanks!
>
> Sebastian

Re: [syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[Namjae Jeon]

[-- Attachment #1: Type: text/plain, Size: 10 bytes --]

#syz test

[-- Attachment #2: 0001-exfat-validate-cluster-allocation-bits-of-bitmap.patch --]
[-- Type: text/x-patch, Size: 3180 bytes --]

From 13c7fa8c637f62ed32ae8231dc395d76503c6fdf Mon Sep 17 00:00:00 2001
From: Namjae Jeon <linkinjeon@kernel.org>
Date: Sat, 30 Aug 2025 14:44:35 +0900
Subject: [PATCH] exfat: validate cluster allocation bits of the allocation bitmap

This patch adds exfat_test_bitmap_range to validate that clusters used for
the allocation bitmap are correctly marked as in-use.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/exfat/balloc.c | 72 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 12 deletions(-)

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index cc01556c9d9b..c09bdb1762f4 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -26,12 +26,55 @@
 /*
  *  Allocation Bitmap Management Functions
  */
+static bool exfat_test_bitmap_range(struct super_block *sb, unsigned int clu,
+		unsigned int count)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	unsigned int start = clu;
+	unsigned int end = clu + count;
+	unsigned int ent_idx, i, b;
+	unsigned int bit_offset, bits_to_check;
+	__le_long *bitmap_le;
+	unsigned long mask, word;
+
+	if (!is_valid_cluster(sbi, start) || !is_valid_cluster(sbi, end - 1))
+		return -EINVAL;
+
+	while (start < end) {
+		ent_idx = CLUSTER_TO_BITMAP_ENT(start);
+		i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
+		b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
+
+		bitmap_le = (__le_long *)sbi->vol_amap[i]->b_data;
+
+		/* Calculate how many bits we can check in the current word */
+		bit_offset = b % BITS_PER_LONG;
+		bits_to_check = min(end - start,
+				    (unsigned int)(BITS_PER_LONG - bit_offset));
+
+		/* Create a bitmask for the range of bits to check */
+		if (bits_to_check >= BITS_PER_LONG)
+			mask = ~0UL;
+		else
+			mask = ((1UL << bits_to_check) - 1) << bit_offset;
+		word = lel_to_cpu(bitmap_le[b / BITS_PER_LONG]);
+
+		/* Check if all bits in the mask are set */
+		if ((word & mask) != mask)
+			return false;
+
+		start += bits_to_check;
+	}
+
+	return true;
+}
+
 static int exfat_allocate_bitmap(struct super_block *sb,
 		struct exfat_dentry *ep)
 {
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	long long map_size;
-	unsigned int i, need_map_size;
+	unsigned int i, j, need_map_size;
 	sector_t sector;
 
 	sbi->map_clu = le32_to_cpu(ep->dentry.bitmap.start_clu);
@@ -58,20 +101,25 @@ static int exfat_allocate_bitmap(struct super_block *sb,
 	sector = exfat_cluster_to_sector(sbi, sbi->map_clu);
 	for (i = 0; i < sbi->map_sectors; i++) {
 		sbi->vol_amap[i] = sb_bread(sb, sector + i);
-		if (!sbi->vol_amap[i]) {
-			/* release all buffers and free vol_amap */
-			int j = 0;
-
-			while (j < i)
-				brelse(sbi->vol_amap[j++]);
-
-			kvfree(sbi->vol_amap);
-			sbi->vol_amap = NULL;
-			return -EIO;
-		}
+		if (!sbi->vol_amap[i])
+			goto err_out;
 	}
 
+	if (exfat_test_bitmap_range(sb, sbi->map_clu,
+		round_up(map_size, sbi->cluster_size) >> sbi->cluster_size_bits) == false)
+		goto err_out;
+
 	return 0;
+
+err_out:
+	j = 0;
+	/* release all buffers and free vol_amap */
+	while (j < i)
+		brelse(sbi->vol_amap[j++]);
+
+	kvfree(sbi->vol_amap);
+	sbi->vol_amap = NULL;
+	return -EIO;
 }
 
 int exfat_load_bitmap(struct super_block *sb)
-- 
2.25.1

Re: [syzbot] [exfat?] [ext4?] WARNING in __rt_mutex_slowlock_locked

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+a725ab460fc1def9896f@syzkaller.appspotmail.com
Tested-by: syzbot+a725ab460fc1def9896f@syzkaller.appspotmail.com

Tested on:

commit:         11e7861d Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13755262580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bd9738e00c1bbfb4
dashboard link: https://syzkaller.appspot.com/bug?extid=a725ab460fc1def9896f
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17b6d634580000

Note: testing is done by a robot and is best-effort only.