Date: Sat, 22 Nov 2025 17:37:19 +0100 From: Michal Meloun <mmel@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: mmap( MAP_ANON) is broken on current. (was Still seeing Failed assertion: "p[i] == 0" on armv7 buildworld) Message-ID: <b94a8938-91e5-41da-9686-03a62ab0142f@freebsd.org> In-Reply-To: <aSHZiASbyd4rqPIV@kib.kiev.ua> References: <8657a2f4-cb32-49a5-bbf6-cd5a4394c7be@FreeBSD.org> <aSAklF9D8haCAaNU@kib.kiev.ua> <aSAq8Ds6nCA24YEI@kib.kiev.ua> <ab87cb06-0b54-431c-9529-1fa993e614ef@freebsd.org> <aSDDatRqKWZ3tUmt@kib.kiev.ua> <aSDFcWRx3vV86KvL@kib.kiev.ua> <07201c46-6fb4-4514-aa88-490830edb010@freebsd.org> <aSG_GJNR7L4Mx-e8@kib.kiev.ua> <aSHDPDsuG40k2TEZ@kib.kiev.ua> <603e75f8-7064-4fca-8520-282331c20ec0@freebsd.org> <aSHZiASbyd4rqPIV@kib.kiev.ua>
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On 22.11.2025 16:40, Konstantin Belousov wrote:
> On Sat, Nov 22, 2025 at 03:31:24PM +0100, Michal Meloun wrote:
>> This patch KASSERTs almost immediately when the system enters multi-user
>> mode while processing mmap() syscall:
>>
>> panic: vm_object_coalesce: obj 0xc73ddb28 next_pindex 0x13 next_size 0x5
>> obj_size 0x176
>
> Yes, the assert was mis-placed. Please try this variant.
>
> commit 2b1a1bcd2926bd89b8422c665b0aa411e29c883b
> Author: Konstantin Belousov <kib@FreeBSD.org>
> Date: Sat Nov 22 16:02:50 2025 +0200
>
> vm_object_coalesce(): fix logic to detect coalesce possibility, simplify
>
> diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
> index 5b4517d2bf0c..9bb4e54edd96 100644
> --- a/sys/vm/vm_object.c
> +++ b/sys/vm/vm_object.c
> @@ -2189,13 +2189,19 @@ vm_object_coalesce(vm_object_t prev_object, vm_ooffset_t prev_offset,
> next_size >>= PAGE_SHIFT;
> next_pindex = OFF_TO_IDX(prev_offset) + prev_size;
>
> - if (prev_object->ref_count > 1 &&
> - prev_object->size != next_pindex &&
> + if (prev_object->ref_count > 1 ||
> + prev_object->size != next_pindex ||
> (prev_object->flags & OBJ_ONEMAPPING) == 0) {
> VM_OBJECT_WUNLOCK(prev_object);
> return (FALSE);
> }
>
> + KASSERT(next_pindex + next_size > prev_object->size,
> + ("vm_object_coalesce: "
> + "obj %p next_pindex %#jx next_size %#jx obj_size %#jx",
> + prev_object, (uintmax_t)next_pindex, (uintmax_t)next_size,
> + (uintmax_t)prev_object->size));
> +
> /*
> * Account for the charge.
> */
> @@ -2222,26 +2228,13 @@ vm_object_coalesce(vm_object_t prev_object, vm_ooffset_t prev_offset,
> * Remove any pages that may still be in the object from a previous
> * deallocation.
> */
> - if (next_pindex < prev_object->size) {
> - vm_object_page_remove(prev_object, next_pindex, next_pindex +
> - next_size, 0);
> -#if 0
> - if (prev_object->cred != NULL) {
> - KASSERT(prev_object->charge >=
> - ptoa(prev_object->size - next_pindex),
> - ("object %p overcharged 1 %jx %jx", prev_object,
> - (uintmax_t)next_pindex, (uintmax_t)next_size));
> - prev_object->charge -= ptoa(prev_object->size -
> - next_pindex);
> - }
> -#endif
> - }
> + vm_object_page_remove(prev_object, next_pindex, next_pindex +
> + next_size, 0);
>
> /*
> * Extend the object if necessary.
> */
> - if (next_pindex + next_size > prev_object->size)
> - prev_object->size = next_pindex + next_size;
> + prev_object->size = next_pindex + next_size;
>
> VM_OBJECT_WUNLOCK(prev_object);
> return (TRUE);
Unfortunately, that didn't help. I will try the vm_map.c patch again
for confirmation.
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