[Bug 294903] zfs: assertion failure: VERIFY3U(offset, <, dn->dn_datablksz) failed (9223372036854775807 < 8704)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294903

Alexander Leidinger <[email protected]> changed:

           What    |Removed                     |Added
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                 CC|                            |[email protected]

--- Comment #3 from Alexander Leidinger <[email protected]> ---
Created attachment 270312
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=270312&action=edit
part of a crashdump output

Here's what I reported about this on current@:
---snip---
recent current (last commit 2026-04-23-222413).

short:
#3  0xffffffff805502f7 in vpanic (
    fmt=0xffffffff82556d5d "VERIFY3U(offset, <, dn->dn_datablksz) failed (%llu
< %llu)\n", ap=ap@entry=0xfffffe0228f57c70)
    at /space/system/usr_src/sys/kern/kern_shutdown.c:974
        buf = "VERIFY3U(offset, <, dn->dn_datablksz) failed
(9223372036854775807 < 24576)\n", '\000' <repeats 180 times>
        __pc = 0x0
        __pc = 0x0
        __pc = 0x0
        other_cpus = {__bits = {16777213, 0 <repeats 15 times>}}
        td = 0xfffff80741b6e780
        bootopt = <unavailable>
        newpanic = <optimized out>

See attachment for a full backtrace. vmcore available.

I can trigger this with a postgresql18 initdb call (I tried an upgrade from
postgresql 17 to 18, copy & paste of the UPDATING entry for the initdb call).
---snip---


And dumbbell@ added there:
---snip---
I get it while working on RabbitMQ as well, 100% reproducible. I shared what I
think I understand of the problem on the pull request that added
POSIX_FADV_DONTNEED support:
https://github.com/openzfs/zfs/pull/18399

However, the patch I drafted, even though it does not cause the panic anymore,
is incorrect as I misunderstood that code.
---snip---

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