Re: Panic: cache_vop_rename: lingering negative entry

> 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);
 		}
 	}