Re: Panic: cache_vop_rename: lingering negative entry

> On 14. Apr 2026, at 17:57, Jan Martin Mikkelsen <janm@transactionware.com> wrote:
> 
> 
>> 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.

https://github.com/openzfs/zfs/pull/18430