Re: Panic: cache_vop_rename: lingering negative entry
Date: Tue, 14 Apr 2026 15:57:43 UTC
> On 14 Apr 2026, at 11:52, Konstantin Belousov <kib@freebsd.org> wrote:
>
> On Tue, Apr 14, 2026 at 11:45:08AM +0200, Jan Martin Mikkelsen wrote:
>>
>>> On 13 Apr 2026, at 22:13, Konstantin Belousov <kib@freebsd.org> wrote:
>>>
>>> On Mon, Apr 13, 2026 at 07:12:32PM +0200, Jan Martin Mikkelsen wrote:
>>>>
>>>>> On 7 Apr 2026, at 20:20, Jan Martin Mikkelsen <janm@transactionware.com> wrote:
>>>>>
>>>>> On 7 Apr 2026, at 18:53, Konstantin Belousov <kib@freebsd.org> wrote:
>>>>>>
>>>>>> On Tue, Apr 07, 2026 at 05:02:05PM +0200, Jan Martin Mikkelsen wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I am consistently getting the panic below while building lang/perl5.42. This is the command from the perl build that triggers the panic:
>>>>>>>
>>>>>>> /usr/bin/strip /ports-work/usr/ports/lang/perl5.42/work/stage/usr/local/bin/perl5.42.0
>>>>>>>
>>>>>>> CURRENT on aarch64, with a kernel from last week, also with a later one from the weekend. A kernel from mid-January worked fine.
>>>>>>>
>>>>>>> I can reproduce on demand, no parallelism in the build required.
>>>>>>>
>>>>>>> Does this look familiar to anyone?
>>>>>>>
>>>>>>> panic: cache_vop_rename: lingering negative entry
>>>>>>> cpuid = 4
>>>>>>> time = 1775410763
>>>>>>> KDB: stack backtrace:
>>>>>>> db_trace_self() at db_trace_self
>>>>>>> db_trace_self_wrapper() at db_trace_self_wrapper+0x38
>>>>>>> vpanic() at vpanic+0x1a0
>>>>>>> panic() at panic+0x48
>>>>>>> cache_vop_rename() at cache_vop_rename+0xb0
>>>>>>> zfs_do_rename() at zfs_do_rename+0xafc
>>>>>>> zfs_freebsd_rename() at zfs_freebsd_rename+0x5c
>>>>>>> VOP_RENAME_APV() at VOP_RENAME_APV+0x44
>>>>>>> kern_renameat () at kern_renameat+0x574
>>>>>>> do_el0_sync() at do_el0_sync+0x5f8
>>>>>>> handle_el0_sync() at handle_el0_sync+0x4c
>>>>>>> --- exception, esr 0x56000000
>>>>>>> KDB: enter: panic
>>>>>>> [ thread pid 81230 tid 101738 ]
>>>>>>> Stopped at kdb_enter+0x48: str xzr, [x19, #3072]
>>>>>>
>>>>>> Is it reproducable on UFS and/or tmpfs?
>>>>>
>>>>> Successful completion (no panic) when the work directory is on UFS, and when the work directory is on tmpfs. I didn’t try multiple times, but it never works on ZFS.
>>>>
>>>> The panic consistently reproduces on a ZFS filesystem with the properties “utf8only=on” and "normalization=formD”.
>>>>
>>>> A ZFS file system with “utf8only=off” and "normalization=none” works fine.
>>>>
>>>> As far as I can see, strip makes a simple rename(2) call, and testing rename(2) works fine (as expected). Running the same strip command on the same files on a fresh system works fine.
>>>>
>>>> The smallest reproducer I have at the moment is building lang/perl5.42.0 with a workdir on a ZFS filesystem enforcing UTF8.
>>>
>>> I am now sure that the reason is that the options you used cause the same
>>> inode to have more than one name (but not hardlinks). I remember that
>>> zfs had option to be case-insensitive, but I may mis-remember.
>>>
>>> The solution, in any case, is to either stop using namecache when these
>>> options are activated, or at least purge all cached entries that has the
>>> given dst when the dst vnode is renamed or deleted.
>>>
>>> Somebody who knows zfs would be needed to make the change.
>>
>> I had a look at the ZFS source, and found this:
>>
>> /*
>> * Only use the name cache if we are looking for a
>> * name on a file system that does not require normalization
>> * or case folding. We can also look there if we happen to be
>> * on a non-normalizing, mixed sensitivity file system IF we
>> * are looking for the exact name (which is always the case on
>> * FreeBSD).
>> */
>> zfsvfs->z_use_namecache = !zfsvfs->z_norm ||
>> ((zfsvfs->z_case == ZFS_CASE_MIXED) &&
>> !(zfsvfs->z_norm & ~U8_TEXTPREP_TOUPPER));
>>
>>
>> The call to cache_vop_rename() which causes the panic is not protected by an “if (zfsvfs->z_use_namecache)”, unlike the rest of the code that uses that to decide whether or not to use the namecache.
>>
>> Elsewhere in zfs_vnops_os.c, there is another call to a cache_vop* function, which is protected by a test:
>>
>> if (zfsvfs->z_use_namecache)
>> cache_vop_rmdir(dvp, vp);
>>
>> It seems to me that this patch could resolve the problem. Does this seem reasonable?
>>
>> --- a/src/sys/contrib/openzfs/module/os/freebsd/zfs/zfs_vnops_os.c 2026-03-28 20:55:06.000000000 1100
>> +++ b/src/sys/contrib/openzfs/module/os/freebsd/zfs/zfs_vnops_os.c 2026-03-28 20:55:06.000000000 1100
>> @@ -3524,7 +3524,7 @@
>> ZRENAMING, NULL));
>> }
>> }
>> - if (error == 0) {
>> + if (error == 0 && zfsvfs->z_use_namecache) {
>> cache_vop_rename(sdvp, *svpp, tdvp, *tvpp, scnp, tcnp);
>> }
>> }
>>
>
> Yes, but please test.
> If works for you, please either create a Github PR or a review on the
> FreeBSD' phab.
That does seem to fix the panic. I’ll do a GitHub PR. Thanks for your help.
Regards,
Jan M.