Date: Fri, 18 Jun 2021 12:19:08 -0700 From: Neel Chauhan <nc@FreeBSD.org> To: Mark Johnston <markj@freebsd.org> Cc: current@freebsd.org Subject: Re: Kernel/driver hacking: panic: Assertion vm_object_busied((m->object)) failed at /usr/src/sys/vm/vm_page.c:5455 Message-ID: <389e4560afdc211e9915746b11a0d0d0@FreeBSD.org> In-Reply-To: <YMymO0fYbsHoK05J@nuc> References: <e542a0c737f24d15df0fadd985e94938@neelc.org> <YMpnf3DcEw6A/rzD@nuc> <8bd27c2a72ebfa9299bca7d930297faf@FreeBSD.org> <YMymO0fYbsHoK05J@nuc>
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Hi Mark,
On 2021-06-18 06:57, Mark Johnston wrote:
> That seems surprising, since the vm_page_grab() call should return the
> page at pidx if one exists.
I believe that's not the case. I did pringfs
>> Any hints on where the physical address is? Should we have an
>> FreeBSD-specific "pa" argument for the physical address if it's
>> needed?
>
> I'm not sure. I'll just note that the Linux code appears to be trying
> to map a set of pages belonging to a scatter-gather list. Taking the
> physical address of the first page and assuming that all subsequent
> pages are physically contiguous doesn't seem correct, but this is what
> is happening in that loop, since each iteration simply increments pa by
> PAGE_SIZE.
Based on this email and our private one, and prior debugging it seems
this panic comes on the first iteration. Something must be
vm_page_grab() returns NULL, and then we run:
if (!vm_page_busy_acquire(m, VM_ALLOC_WAITFAIL))
goto retry;
if (vm_page_insert(m, vm_obj, pidx)) {
vm_page_xunbusy(m);
VM_OBJECT_WUNLOCK(vm_obj);
vm_wait(NULL);
VM_OBJECT_WLOCK(vm_obj);
goto retry;
}
Source:
https://github.com/neelchauhan/drm-kmod/blob/d0eee96973ee0772e977b813678f92c5becf0507/drivers/gpu/drm/i915/intel_freebsd.c#L245
The first if() doesn't panic, but we panic at the second one, it doesn't
go into or jumo over the statement.
I could use for() or for_each_sg_page() and they both panic.
I am almost feeling I'd have to hire a FreeBSD kernel consultant and/or
sell my TigerLake laptop for an AMD Ryzen-based laptop.
-Neel (nc@)
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