Hi,
I've encountered a few NULL pointer dereference bugs while running a
custom test case on btrfs (kernel 3.11.1), inside a QEMU based VM.
Btrfs was statically compiled and the btrfs filesystem was mounted on
one or two loop devices. All cases occurred during execution of a
"filesystem balance" operation and while another file system operation
was concurrently executed. In one case the other operation was a "mknod"
and in another it was a "filesystem show" operation.
In all cases the NULL pointer dereference occurred in the
"btrfs_find_all_roots" function and all cases produced a bug report
similar to the one bellow:
[ 138.573390] BUG: unable to handle kernel NULL pointer dereference
at (null)
[ 138.573390] IP: [<c12feeb3>] ulist_next+0x4/0x26
[ 138.573390] *pde = 00000000
[ 138.573390] Oops: 0000 [#1] SMP
[ 138.573390] Modules linked in: loop rtc_cmos pcspkr tpm_tis
freq_table mperf i2c_piix4
[ 138.573390] CPU: 0 PID: 2794 Comm: btrfs-endio-wri Not tainted
3.11.1 #2
[ 138.573390] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
[ 138.573390] task: c5dea6b0 ti: c5e12000 task.ti: c5e12000
[ 138.573390] EIP: 0060:[<c12feeb3>] EFLAGS: 00000246 CPU: 0
[ 138.573390] EIP is at ulist_next+0x4/0x26
[ 138.573390] EAX: 00000000 EBX: 00000000 ECX: d9c29e38 EDX: c5e13da4
[ 138.573390] ESI: 00000000 EDI: c5e13e00 EBP: c5e13d94 ESP: c5e13d90
[ 138.573390] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[ 138.573390] CR0: 8005003b CR2: 00000000 CR3: 059d8000 CR4: 00000690
[ 138.573390] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 138.573390] DR6: 00000000 DR7: 00000000
[ 138.573390] Stack:
[ 138.573390] 00000000 c5e13db4 c12fe7b8 de4d1000 d9cead48 00000001
010dd000 deeab810
[ 138.573390] 00000001 c5e13e10 c12fe8cf 00af2000 00000000 00000000
00000003 c5e13e00
[ 138.573390] deeabe00 00000000 00000003 deeab800 de4d1000 d9cead48
de4d14b8 de4d14b8
[ 138.573390] Call Trace:
[ 138.573390] [<c12fe7b8>] btrfs_find_all_roots+0x88/0xa6
[ 138.573390] [<c12fe8cf>] iterate_extent_inodes+0xf9/0x1b2
[ 138.573390] [<c12feba9>] iterate_inodes_from_logical+0x88/0x97
[ 138.573390] [<c12b8880>] ? record_extent_backrefs+0x8b/0x8b
[ 138.573390] [<c12b8845>] record_extent_backrefs+0x50/0x8b
[ 138.573390] [<c12b8880>] ? record_extent_backrefs+0x8b/0x8b
[ 138.573390] [<c12c1f8e>] btrfs_finish_ordered_io+0x77e/0x876
[ 138.573390] [<c12c2091>] finish_ordered_fn+0xb/0xd
[ 138.573390] [<c12db161>] worker_loop+0x111/0x3ec
[ 138.573390] [<c104a2c4>] ? default_wake_function+0xb/0xd
[ 138.573390] [<c1040c43>] kthread+0x90/0x95
[ 138.573390] [<c12db050>] ? btrfs_queue_worker+0x1c8/0x1c8
[ 138.573390] [<c176c277>] ret_from_kernel_thread+0x1b/0x28
[ 138.573390] [<c1040bb3>] ? kthread_freezable_should_stop+0x4f/0x4f
[ 138.573390] Code: 5b 5e 5f 5d c3 90 90 90 55 8d 50 10 89 e5 c7 00
00 00 00 00 89 50 08 c7 40 04 10 00 00 00 c7 40 0c 00 00 00 00 5d c3
55 89 e5 53 <8b> 08 85 c9 74 15 8b 1a 85 db 78 0f 39 cb 73 0b 6b cb 1c
43 03
[ 138.573390] EIP: [<c12feeb3>] ulist_next+0x4/0x26 SS:ESP 0068:c5e13d90
[ 138.573390] CR2: 0000000000000000
[ 138.573390] ---[ end trace 626899e11111abbe ]---
[ 138.573390] BUG: unable to handle kernel NULL pointer dereference
at (null)
[ 138.573390] IP: [<c12feeb3>] ulist_next+0x4/0x26
[ 138.573390] *pde = 00000000
[ 138.573390] Oops: 0000 [#2] SMP
[ 138.573390] Modules linked in: loop rtc_cmos pcspkr tpm_tis
freq_table mperf i2c_piix4
[ 138.573390] CPU: 1 PID: 2793 Comm: btrfs-endio-wri Tainted: G
D 3.11.1 #2
[ 138.573390] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
[ 138.573390] task: c59cc190 ti: dedc8000 task.ti: dedc8000
[ 138.573390] EIP: 0060:[<c12feeb3>] EFLAGS: 00000246 CPU: 1
[ 138.573390] EIP is at ulist_next+0x4/0x26
[ 138.573390] EAX: 00000000 EBX: 00000000 ECX: d9c296c8 EDX: dedc9da4
[ 138.573390] ESI: 00000000 EDI: dedc9e00 EBP: dedc9d94 ESP: dedc9d90
[ 138.573390] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[ 138.573390] CR0: 8005003b CR2: 00000000 CR3: 03ebe000 CR4: 00000690
[ 138.573390] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 138.573390] DR6: 00000000 DR7: 00000000
[ 138.573390] Stack:
[ 138.573390] 00000000 dedc9db4 c12fe7b8 de4d1000 d9ceaf50 00000001
00dea000 de4c6410
[ 138.573390] 00000001 dedc9e10 c12fe8cf 00af2000 00000000 00000000
00000005 dedc9e00
[ 138.573390] de4c6c00 00000000 00000005 de4c6400 de4d1000 d9ceaf50
de4d14b8 c5e13de8
[ 138.573390] Call Trace:
[ 138.573390] [<c12fe7b8>] btrfs_find_all_roots+0x88/0xa6
[ 138.573390] [<c12fe8cf>] iterate_extent_inodes+0xf9/0x1b2
[ 138.573390] [<c12feba9>] iterate_inodes_from_logical+0x88/0x97
[ 138.573390] [<c12b8880>] ? record_extent_backrefs+0x8b/0x8b
[ 138.573390] [<c12b8845>] record_extent_backrefs+0x50/0x8b
[ 138.573390] [<c12b8880>] ? record_extent_backrefs+0x8b/0x8b
[ 138.573390] [<c12c1f8e>] btrfs_finish_ordered_io+0x77e/0x876
[ 138.573390] [<c12c2091>] finish_ordered_fn+0xb/0xd
[ 138.573390] [<c12db161>] worker_loop+0x111/0x3ec
[ 138.573390] [<c104a2c4>] ? default_wake_function+0xb/0xd
[ 138.573390] [<c1040c43>] kthread+0x90/0x95
[ 138.573390] [<c12db050>] ? btrfs_queue_worker+0x1c8/0x1c8
[ 138.573390] [<c176c277>] ret_from_kernel_thread+0x1b/0x28
[ 138.573390] [<c1040bb3>] ? kthread_freezable_should_stop+0x4f/0x4f
[ 138.573390] Code: 5b 5e 5f 5d c3 90 90 90 55 8d 50 10 89 e5 c7 00
00 00 00 00 89 50 08 c7 40 04 10 00 00 00 c7 40 0c 00 00 00 00 5d c3
55 89 e5 53 <8b> 08 85 c9 74 15 8b 1a 85 db 78 0f 39 cb 73 0b 6b cb 1c
43 03
[ 138.573390] EIP: [<c12feeb3>] ulist_next+0x4/0x26 SS:ESP 0068:dedc9d90
[ 138.573390] CR2: 0000000000000000
[ 138.573390] ---[ end trace 626899e11111abbf ]---
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