Bug 277538

Summary:	panic: vm_page_assert_unbusied: busy_lock owned by me
Product:	Base System	Reporter:	John F. Carr <jfc>
Component:	kern	Assignee:	Mark Johnston <markj>
Status:	Closed FIXED
Severity:	Affects Only Me	CC:	kib, markj
Priority:	---	Keywords:	crash
Version:	15.0-CURRENT
Hardware:	Any
OS:	Any

Description John F. Carr 2024-03-06 20:17:46 UTC

Rebooting after removing a swap device caused a panic

panic: vm_page_assert_unbusied: page 0xffffa000e7d451e0 busy_lock 0xd6ba02c2 owned by me (0xffff0000d6ba02c0) @ /usr/src/sys/vm/vm_object.c:897

Longer version:

I unplugged a USB drive from an arm64 SBC (RockPro64).  It contained the swap device so the system was not happy.  I plugged it back in but the system did not understand that the device I plugged in was the same device I removed.  I could not "swapoff" to get the data off the drive.  I rebooted and got the panic above.

I am running a recent 15.0-CURRENT based on c6a6ec85a70314b8270e25a06e77e2e7c95c7055.

No crash dump.  The kernel debugger hung when I asked it to dump.  It probably could not figure out where to dump.  Here is the text on the console:

[unplugged swap device]

# swapinfo
Device          1K-blocks     Used    Avail Capacity
/dev/#C:0xb2      8069120    26852  8042268     0%

[plugged device back in]

# swapinfo
Device          1K-blocks     Used    Avail Capacity
/dev/#C:0xb2      8069120    26852  8042268     0%
root@variegatus:~ # reboot
Mar  6 20:03:25 variegatus reboot[80617]: rebooted by root
swap_pager: I/O error - pagein failed; blkno 3033084,size 4096, error 6
vm_fault: pager read error, pid 50404 (sshd)
swap_pager: I/O error - pagein failed; blkno 3033109,size 4096, error 6
vm_fault: pager read error, pid 50402 (sshd)
swap_pager: I/O error - pagein failed; blkno 2793364,size 8192, error 6
swap_pager: I/O error - pagein failed; blkno 2793378,size 8192, error 6
swap_pager: I/O error - pagein failed; blkno 2793340,size 8192, error 6
vm_fault: pager read error, pid 2600 (getty)
vm_fault: pager read error, pid 2602 (getty)
swap_pager: I/O error - pagein failed; blkno 2797106,size 8192, error 6
swap_pager: I/O error - pagein failed; blkno 2793206,size 8192, error 6
swap_pager: I/O error - pagein failed; blkno 2793359,size 20480, error 6
vm_fault: pager read error, pid 87805 (sshd)
vm_fault: pager read error, pid 2599 (getty)
vm_fault: pager read error, pid 2601 (getty)
vm_fault: pager read error, pid 2600 (getty)
panic: vm_page_assert_unbusied: page 0xffffa000e7d451e0 busy_lock 0xd6ba02c2 owned by me (0xffff0000d6ba02c0) @ /usr/src/sys/vm/vm_object.c:897
cpuid = 4
time = 1709755406
KDB: stack backtrace:
db_trace_self() at db_trace_self
db_trace_self_wrapper() at db_trace_self_wrapper+0x38
vpanic() at vpanic+0x1a8
panic() at panic+0x48
vm_object_terminate() at vm_object_terminate+0x2a4
vm_object_deallocate() at vm_object_deallocate+0x2cc
vm_map_process_deferred() at vm_map_process_deferred+0xa8
vm_map_remove() at vm_map_remove+0xc8
vmspace_exit() at vmspace_exit+0x138
exit1() at exit1+0x4e8
sigexit() at sigexit+0x154
postsig() at postsig+0x11c
ast_sig() at ast_sig+0x128
ast_handler() at ast_handler+0xc8
ast() at ast+0x24
handle_el0_sync() at handle_el0_sync+0x6c
--- exception, esr 0x56000000
KDB: enter: panic
[ thread pid 87805 tid 100300 ]

Comment 1 Konstantin Belousov freebsd_committer

2024-03-07 00:29:43 UTC

If an error occured during page-in, swap pager leaves the page invalid and busy.
This is reasonable approach.

If something is paged out, and we cannot page it in, system is going to be
unhappy.  I am not sure it would help add more code that is almost never
executed and very hard to test, to try to slightly soften the consequences.

Comment 2 Mark Johnston freebsd_committer

2024-04-05 19:08:37 UTC

(In reply to Konstantin Belousov from comment #1)
I think there is still a bug in that swap_pager_iodone() does not unbusy readahead/behind pages in the error case.

Comment 3 Mark Johnston freebsd_committer

2024-04-05 19:17:18 UTC

https://reviews.freebsd.org/D44646

Comment 4 commit-hook freebsd_committer

2024-04-08 13:15:38 UTC

A commit in branch main references this bug:

URL: https://cgit.FreeBSD.org/src/commit/?id=4696650782e2e5cf7ae5823f1de04550c05b5b75

commit 4696650782e2e5cf7ae5823f1de04550c05b5b75
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2024-04-08 13:02:48 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2024-04-08 13:02:48 +0000

    swap_pager: Unbusy readahead pages after an I/O error

    The swap pager itself allocates readahead pages, so should take care to
    unbusy them after a read error, just as it does in the non-error case.

    PR:             277538
    Reviewed by:    olce, dougm, alc, kib
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D44646

 sys/vm/swap_pager.c | 3 +++
 1 file changed, 3 insertions(+)

Comment 5 Mark Johnston freebsd_committer

2024-04-08 13:17:11 UTC

I believe that this commit will prevent that particular panic, but indeed, we're not going to recover well from a swap device being removed.

Comment 6 commit-hook freebsd_committer

2024-04-15 14:06:02 UTC

A commit in branch stable/14 references this bug:

URL: https://cgit.FreeBSD.org/src/commit/?id=5128c8948b4e56d20dfd623aeb030fb39c8f95b0

commit 5128c8948b4e56d20dfd623aeb030fb39c8f95b0
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2024-04-08 13:02:48 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2024-04-15 14:05:13 +0000

    swap_pager: Unbusy readahead pages after an I/O error

    The swap pager itself allocates readahead pages, so should take care to
    unbusy them after a read error, just as it does in the non-error case.

    PR:             277538
    Reviewed by:    olce, dougm, alc, kib
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D44646

    (cherry picked from commit 4696650782e2e5cf7ae5823f1de04550c05b5b75)

 sys/vm/swap_pager.c | 3 +++
 1 file changed, 3 insertions(+)

Comment 7 Mark Johnston freebsd_committer

2024-10-10 16:00:05 UTC

Closing this since the bug causing the panic is fixed, at least.