[syzbot] [btrfs?] kernel BUG in __extent_writepage_io (2)

Hello,

syzbot found the following issue on:

HEAD commit: d2bafcf224f3 Merge tag 'cgroup-for-6.11-rc4-fixes' of git:..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12d5fa7b980000
kernel config: https://syzkaller.appspot.com/x/.config?x=4fc2afd52fd008bb
dashboard link: https://syzkaller.appspot.com/bug?extid=ba3c0273042a898c230e
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=137c040b980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16ddb015980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7569f02310fb/disk-d2bafcf2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e30fee7b6c1d/vmlinux-d2bafcf2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2ffddebac153/bzImage-d2bafcf2.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/cd08557ae343/mount_0.gz
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/90ff8392fe84/mount_2.gz
mounted in repro #3: https://storage.googleapis.com/syzbot-assets/9c5b91850930/mount_7.gz

The issue was bisected to:

commit f22b5dcbd71edea087946511554956591557de9a
Author: Christoph Hellwig <[email protected]>
Date: Wed May 31 06:04:59 2023 +0000

btrfs: remove non-standard extent handling in __extent_writepage_io

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10974043980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=12974043980000
console output: https://syzkaller.appspot.com/x/log.txt?x=14974043980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]
Fixes: f22b5dcbd71e ("btrfs: remove non-standard extent handling in __extent_writepage_io")

assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1488
------------[ cut here ]------------
kernel BUG at fs/btrfs/extent_io.c:1488!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 1 UID: 0 PID: 5722 Comm: syz-executor399 Not tainted 6.11.0-rc4-syzkaller-00255-gd2bafcf224f3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
RIP: 0010:__extent_writepage_io+0x1224/0x1400 fs/btrfs/extent_io.c:1488
Code: f7 07 90 0f 0b e8 dc 68 df fd 48 c7 c7 e0 92 2c 8c 48 c7 c6 c0 a0 2c 8c 48 c7 c2 80 92 2c 8c b9 d0 05 00 00 e8 9d 15 f7 07 90 <0f> 0b e8 b5 68 df fd 48 8b 3c 24 e8 bc 9d ff ff 48 89 c7 48 c7 c6
RSP: 0018:ffffc900097d6ee8 EFLAGS: 00010246
RAX: 000000000000004e RBX: 0000000000000000 RCX: 2f9fd79be1350f00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffffffff817402ac R09: 1ffff920012fad7c
R10: dffffc0000000000 R11: fffff520012fad7d R12: ffffea0001ccbdc8
R13: 1ffffd40003997b9 R14: fffffffffffffffd R15: 000000000007b000
FS: 00007f11a84976c0(0000) GS:ffff8880b9300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f11a0fff000 CR3: 0000000020e4c000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__extent_writepage fs/btrfs/extent_io.c:1578 [inline]
extent_write_cache_pages fs/btrfs/extent_io.c:2251 [inline]
btrfs_writepages+0x12a2/0x2760 fs/btrfs/extent_io.c:2373
do_writepages+0x35d/0x870 mm/page-writeback.c:2683
filemap_fdatawrite_wbc+0x125/0x180 mm/filemap.c:397
__filemap_fdatawrite_range mm/filemap.c:430 [inline]
filemap_fdatawrite_range+0x120/0x180 mm/filemap.c:448
btrfs_fdatawrite_range+0x53/0xe0 fs/btrfs/file.c:3794
btrfs_direct_write+0x558/0xb40 fs/btrfs/direct-io.c:952
btrfs_do_write_iter+0x2a1/0x760 fs/btrfs/file.c:1505
do_iter_readv_writev+0x60a/0x890
vfs_writev+0x37c/0xbb0 fs/read_write.c:971
do_pwritev fs/read_write.c:1072 [inline]
__do_sys_pwritev2 fs/read_write.c:1131 [inline]
__se_sys_pwritev2+0x1ca/0x2d0 fs/read_write.c:1122
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f11a850bd79
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 1d 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f11a8497158 EFLAGS: 00000212 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007f11a85916d8 RCX: 00007f11a850bd79
RDX: 0000000000000001 RSI: 0000000020000240 RDI: 0000000000000004
RBP: 00007f11a85916d0 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000002000 R11: 0000000000000212 R12: 00007f11a85916dc
R13: 000000000000006e R14: 00007ffd9dcad860 R15: 00007ffd9dcad948
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__extent_writepage_io+0x1224/0x1400 fs/btrfs/extent_io.c:1488
Code: f7 07 90 0f 0b e8 dc 68 df fd 48 c7 c7 e0 92 2c 8c 48 c7 c6 c0 a0 2c 8c 48 c7 c2 80 92 2c 8c b9 d0 05 00 00 e8 9d 15 f7 07 90 <0f> 0b e8 b5 68 df fd 48 8b 3c 24 e8 bc 9d ff ff 48 89 c7 48 c7 c6
RSP: 0018:ffffc900097d6ee8 EFLAGS: 00010246
RAX: 000000000000004e RBX: 0000000000000000 RCX: 2f9fd79be1350f00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffffffff817402ac R09: 1ffff920012fad7c
R10: dffffc0000000000 R11: fffff520012fad7d R12: ffffea0001ccbdc8
R13: 1ffffd40003997b9 R14: fffffffffffffffd R15: 000000000007b000
FS: 00007f11a84976c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005654e2821068 CR3: 0000000020e4c000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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 [email protected].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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

This means there is a dirty page range for us to writeback, but no
delalloc range for it.

That patch is not the cause, but only exposed it.

I guess there is some page fault involved or interrupted direct IO?

Anyway the bisection doesn't make much sense.

Thanks,
Qu

#syz test

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 744e8952abb0..c81b23d0d73e 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -262,6 +262,7 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
em->len += merge->len;
em->block_len += merge->block_len;
em->block_start = merge->block_start;
+ printk("em: %p, blockstart: %llu, mblockstart: %llu, %s\n", em, em->block_start, merge->block_start, __func__);
em->generation = max(em->generation, merge->generation);
em->flags |= EXTENT_FLAG_MERGED;

@@ -393,7 +394,11 @@ static int add_extent_mapping(struct btrfs_inode *inode,
if (ret)
return ret;

+ printk("em: %p, blockstart: %llu, em refs: %d, %s\n",
+ em, em->block_start, refcount_read(&em->refs), __func__);
setup_extent_mapping(inode, em, modified);
+ printk("setuped, em: %p, blockstart: %llu, em refs: %d, %s\n",
+ em, em->block_start, refcount_read(&em->refs), __func__);

if (!btrfs_is_testing(fs_info) && is_fstree(btrfs_root_id(root)))
percpu_counter_inc(&fs_info->evictable_extent_maps);
@@ -643,6 +648,8 @@ int btrfs_add_extent_mapping(struct btrfs_inode *inode,
}
free_extent_map(existing);
}
+ } else if (!ret) {
+ ASSERT(em->block_start != EXTENT_MAP_HOLE);
}

ASSERT(ret == 0 || ret == -EEXIST);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3a2b902b2d1f..b588381458df 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6972,7 +6972,9 @@ struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
}

write_lock(&em_tree->lock);
+ printk("em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", em, em->block_start, start, len, __func__);
ret = btrfs_add_extent_mapping(inode, &em, start, len);
+ printk("ret: %d, em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", ret, em, em->block_start, start, len, __func__);
write_unlock(&em_tree->lock);
out:
btrfs_free_path(path);

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file fs/btrfs/extent_map.c
Hunk #1 FAILED at 262.
Hunk #2 succeeded at 493 (offset 100 lines).
Hunk #3 succeeded at 747 (offset 100 lines).
1 out of 3 hunks FAILED
checking file fs/btrfs/inode.c
Hunk #1 succeeded at 6958 (offset -14 lines).



Tested on:

commit: d5d547aa Merge tag 'random-6.11-rc6-for-linus' of git:..
git tree: upstream
patch: https://syzkaller.appspot.com/x/patch.diff?x=1448bceb980000

index 10ac5f657e38..3a6d2b758587 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -384,6 +384,7 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
free_extent_map(merge);
dec_evictable_extent_maps(inode);
/*
@@ -493,7 +494,11 @@ static int add_extent_mapping(struct btrfs_inode *inode,
@@ -743,6 +748,8 @@ int btrfs_add_extent_mapping(struct btrfs_inode *inode,
index b1b6564ab68f..d54c8d2ff1c1 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6958,7 +6958,9 @@ struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,

fs/btrfs/inode.c:6961:75: error: no member named 'block_start' in 'struct extent_map'
fs/btrfs/inode.c:6963:89: error: no member named 'block_start' in 'struct extent_map'
patch: https://syzkaller.appspot.com/x/patch.diff?x=1230ffa3980000

index 10ac5f657e38..397eee4c4217 100644
+ printk("em: %p, blockstart: %llu, mblockstart: %llu, %s\n", em, extent_map_block_start(em), extent_map_block_start(merge), __func__);
+ em, extent_map_block_start(em), refcount_read(&em->refs), __func__);
+ em, extent_map_block_start(em), refcount_read(&em->refs), __func__);
+ ASSERT(extent_map_block_start(em) != EXTENT_MAP_HOLE);
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index 5154a8f1d26c..a84ef0c7d601 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -154,6 +154,7 @@ static inline u64 extent_map_block_start(const struct extent_map *em)
if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
if (extent_map_is_compressed(em))
return em->disk_bytenr;
+ printk("em: %p, disk byte nr: %llu, offset: %llu, %s\n", em, em->disk_bytenr, em->offset, __func__);
return em->disk_bytenr + em->offset;
}
return em->disk_bytenr;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b1b6564ab68f..45f3b31aacc3 100644
+ printk("em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", em, extent_map_block_start(em), start, len, __func__);
+ printk("ret: %d, em: %p, blockstart: %llu, start: %llu, len: %llu, %s\n", ret, em, extent_map_block_start(em), start, len, __func__);
write_unlock(&em_tree->lock);
out:
btrfs_free_path(path);

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in btrfs_add_extent_mapping

em: ffff888066d637e0, blockstart: 18446744073709551613, em refs: 1, add_extent_mapping
em: ffff888066d637e0, blockstart: 18446744073709551613, mblockstart: 18446744073709551613, try_merge_map
setuped, em: ffff888066d637e0, blockstart: 18446744073709551613, em refs: 2, add_extent_mapping
assertion failed: extent_map_block_start(em) != EXTENT_MAP_HOLE, in fs/btrfs/extent_map.c:752
------------[ cut here ]------------
kernel BUG at fs/btrfs/extent_map.c:752!
CPU: 0 UID: 0 PID: 6365 Comm: syz.1.20 Not tainted 6.11.0-rc5-syzkaller-00081-gd5d547aa7b51-dirty #0
RIP: 0010:btrfs_add_extent_mapping+0x715/0x790 fs/btrfs/extent_map.c:752
Code: f9 07 90 0f 0b e8 8b e6 e1 fd 48 c7 c7 20 5b 2c 8c 48 c7 c6 20 5c 2c 8c 48 c7 c2 a0 59 2c 8c b9 f0 02 00 00 e8 2c c5 f9 07 90 <0f> 0b e8 64 e6 e1 fd 49 be 00 00 00 00 00 fc ff df e9 6a fb ff ff
RSP: 0018:ffffc900032b7160 EFLAGS: 00010246
RAX: 000000000000005d RBX: dffffc0000000000 RCX: 10a2bc291a71c100
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 1ffff1100cdac701 R08: ffffffff817400cc R09: fffffbfff1cba0e0
R10: dffffc0000000000 R11: fffffbfff1cba0e0 R12: ffff888066d63808
R13: ffff888066d637e0 R14: 0000000000000000 R15: fffffffffffffffd
FS: 00007f3abd3676c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CR2: 00007fffd35749c8 CR3: 0000000074d68000 CR4: 00000000003506f0
btrfs_get_extent+0x124b/0x1d30 fs/btrfs/inode.c:6962
btrfs_cont_expand+0x28f/0xcd0 fs/btrfs/inode.c:4923
btrfs_write_check+0x440/0x590 fs/btrfs/file.c:1181
btrfs_buffered_write+0x288/0x1360 fs/btrfs/file.c:1221
btrfs_direct_write+0x531/0xb40 fs/btrfs/direct-io.c:942
RIP: 0033:0x7f3abc579e79
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:00007f3abd367038 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007f3abc716058 RCX: 00007f3abc579e79
RBP: 00007f3abc5e793e R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000002000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f3abc716058 R15: 00007ffe16a6f238
RIP: 0010:btrfs_add_extent_mapping+0x715/0x790 fs/btrfs/extent_map.c:752
Code: f9 07 90 0f 0b e8 8b e6 e1 fd 48 c7 c7 20 5b 2c 8c 48 c7 c6 20 5c 2c 8c 48 c7 c2 a0 59 2c 8c b9 f0 02 00 00 e8 2c c5 f9 07 90 <0f> 0b e8 64 e6 e1 fd 49 be 00 00 00 00 00 fc ff df e9 6a fb ff ff
RSP: 0018:ffffc900032b7160 EFLAGS: 00010246
RAX: 000000000000005d RBX: dffffc0000000000 RCX: 10a2bc291a71c100
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 1ffff1100cdac701 R08: ffffffff817400cc R09: fffffbfff1cba0e0
R10: dffffc0000000000 R11: fffffbfff1cba0e0 R12: ffff888066d63808
R13: ffff888066d637e0 R14: 0000000000000000 R15: fffffffffffffffd
FS: 00007f3abd3676c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CR2: 00007fffd35749c8 CR3: 0000000074d68000 CR4: 00000000003506f0
console output: https://syzkaller.appspot.com/x/log.txt?x=1266cceb980000
kernel config: https://syzkaller.appspot.com/x/.config?x=a0455552d0b27491
patch: https://syzkaller.appspot.com/x/patch.diff?x=11df82eb980000

index 10ac5f657e38..fc6e83c6e69b 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -384,6 +384,8 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
free_extent_map(merge);
dec_evictable_extent_maps(inode);
}
+ printk("em: %p, blockstart: %llu, mblockstart: %llu, merged: %d, %s\n", em,
+ extent_map_block_start(em), extent_map_block_start(merge), em->flags & EXTENT_FLAG_MERGED, __func__);
}

/*
@@ -493,7 +495,11 @@ static int add_extent_mapping(struct btrfs_inode *inode,
@@ -743,6 +749,11 @@ int btrfs_add_extent_mapping(struct btrfs_inode *inode,
+ if (em->flags & EXTENT_FLAG_MERGED)
+ ASSERT(extent_map_block_start(em) != EXTENT_MAP_HOLE);
+ else
+ return -EINVAL;

general protection fault in try_merge_map

em: ffff88802539cdc8, blockstart: 18446744073709551613, start: 0, len: 503808, btrfs_get_extent
em: ffff88802539cdc8, blockstart: 18446744073709551613, em refs: 1, add_extent_mapping
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 1 UID: 0 PID: 6499 Comm: syz.4.24 Not tainted 6.11.0-rc5-syzkaller-00081-gd5d547aa7b51-dirty #0
RIP: 0010:extent_map_block_start fs/btrfs/extent_map.h:154 [inline]
RIP: 0010:try_merge_map+0x684/0x8e0 fs/btrfs/extent_map.c:387
Code: 19 e8 a0 f9 e1 fd 48 8b 2c 24 eb 0e e8 95 f9 e1 fd 48 8b 2c 24 4c 8b 64 24 10 48 83 c5 28 48 89 e8 48 c1 e8 03 48 89 44 24 20 <42> 80 3c 38 00 74 08 48 89 ef e8 4d 16 46 fe 48 89 6c 24 18 48 8b
RSP: 0018:ffffc90008e8f2c0 EFLAGS: 00010206
RAX: 0000000000000005 RBX: ffff88802539cdc8 RCX: ffff88802b4e0000
RDX: 0000000000000000 RSI: fffffffffffffffd RDI: fffffffffffffffc
RBP: 0000000000000028 R08: ffffffff83b19139 R09: 1ffff11004a739c3
R10: dffffc0000000000 R11: ffffed1004a739c4 R12: fffffffffffffffd
R13: ffff88802539ce18 R14: 1ffff11004a739c3 R15: dffffc0000000000
FS: 00007f6c742e86c0(0000) GS:ffff8880b9300000(0000) knlGS:0000000000000000
CR2: 00007f6c742e7f98 CR3: 00000000221cc000 CR4: 00000000003506f0
setup_extent_mapping fs/btrfs/extent_map.c:467 [inline]
add_extent_mapping+0x604/0xa50 fs/btrfs/extent_map.c:500
btrfs_add_extent_mapping+0x10e/0x7b0 fs/btrfs/extent_map.c:712
btrfs_direct_write+0x2f1/0xb40 fs/btrfs/direct-io.c:818
RIP: 0033:0x7f6c73579e79
RSP: 002b:00007f6c742e8038 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007f6c73716058 RCX: 00007f6c73579e79
RBP: 00007f6c735e793e R08: 0000000000000000 R09: 0000000000000003
R13: 0000000000000000 R14: 00007f6c73716058 R15: 00007ffed77574b8
RIP: 0010:extent_map_block_start fs/btrfs/extent_map.h:154 [inline]
RIP: 0010:try_merge_map+0x684/0x8e0 fs/btrfs/extent_map.c:387
Code: 19 e8 a0 f9 e1 fd 48 8b 2c 24 eb 0e e8 95 f9 e1 fd 48 8b 2c 24 4c 8b 64 24 10 48 83 c5 28 48 89 e8 48 c1 e8 03 48 89 44 24 20 <42> 80 3c 38 00 74 08 48 89 ef e8 4d 16 46 fe 48 89 6c 24 18 48 8b
RSP: 0018:ffffc90008e8f2c0 EFLAGS: 00010206
RAX: 0000000000000005 RBX: ffff88802539cdc8 RCX: ffff88802b4e0000
RDX: 0000000000000000 RSI: fffffffffffffffd RDI: fffffffffffffffc
RBP: 0000000000000028 R08: ffffffff83b19139 R09: 1ffff11004a739c3
R10: dffffc0000000000 R11: ffffed1004a739c4 R12: fffffffffffffffd
R13: ffff88802539ce18 R14: 1ffff11004a739c3 R15: dffffc0000000000
FS: 00007f6c742e86c0(0000) GS:ffff8880b9300000(0000) knlGS:0000000000000000
CR2: 00007f6c742e7f98 CR3: 00000000221cc000 CR4: 00000000003506f0
----------------
Code disassembly (best guess), 1 bytes skipped:
0: e8 a0 f9 e1 fd call 0xfde1f9a5
5: 48 8b 2c 24 mov (%rsp),%rbp
9: eb 0e jmp 0x19
b: e8 95 f9 e1 fd call 0xfde1f9a5
10: 48 8b 2c 24 mov (%rsp),%rbp
14: 4c 8b 64 24 10 mov 0x10(%rsp),%r12
19: 48 83 c5 28 add $0x28,%rbp
1d: 48 89 e8 mov %rbp,%rax
20: 48 c1 e8 03 shr $0x3,%rax
24: 48 89 44 24 20 mov %rax,0x20(%rsp)
* 29: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 48 89 ef mov %rbp,%rdi
33: e8 4d 16 46 fe call 0xfe461685
38: 48 89 6c 24 18 mov %rbp,0x18(%rsp)
3d: 48 rex.W
3e: 8b .byte 0x8b
console output: https://syzkaller.appspot.com/x/log.txt?x=1162fc35980000
patch: https://syzkaller.appspot.com/x/patch.diff?x=1166fa0b980000

index 10ac5f657e38..4e2c30acca67 100644
+ printk("em: %p, blockstart: %llu, mblockstart: %llu, %s\n", em,
+ extent_map_block_start(em), em->flags & EXTENT_FLAG_MERGED, __func__);

Hello,

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

Reported-by: [email protected]
Tested-by: [email protected]
console output: https://syzkaller.appspot.com/x/log.txt?x=167ccf8d980000
patch: https://syzkaller.appspot.com/x/patch.diff?x=10dcde33980000

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