Date: Fri, 4 Apr 2003 10:03:30 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Nate Lawson <nate@root.org> Cc: jake@freebsd.org Subject: Giant required by uma (was Re: mbuf LOR) Message-ID: <16013.40642.784712.453084@grasshopper.cs.duke.edu> In-Reply-To: <Pine.BSF.4.21.0304040001330.15815-100000@root.org> References: <16012.32534.331966.216694@grasshopper.cs.duke.edu> <Pine.BSF.4.21.0304040001330.15815-100000@root.org>
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Nate Lawson writes:
>
> You're right about where the problem is (top of stack trace and listing
> below). However, your patch causes an immediate panic on boot due to a
> NULL deref. I don't think you want it to always return NULL if called
> with M_NOWAIT set. :) Other ideas?
>
I suppose the only alternative is to "do it right" and remove Giant
from the uma zone alloc code.
>From looking at the code for a little while this morning, it looks
like there are 3 allocators that could be called at this point in the
code:
1) page_alloc():
Calls kmem_malloc(). Should be MPSAFE on NOWAIT allocations. Needs
Giant on WAITOK allocations.
2) obj_alloc():
Calls vm_page_alloc() -- that's MPSAFE.
Calls pmap_qenter() -- I've got no freaking clue if that's MPSAFE on
all platforms. I think it is, since kmem_malloc is MPSAFE & it
calls pmap_enter(), but I'm not sure.
uma_small_alloc():
i386 - no uma_small_alloc, no problem
alpha - uma_small_alloc is SMP safe
ia64 - uma_small_alloc should be SMP safe, as it seems to be
doing just the moral equivalent of PHYS_TO_K0SEG() to map the memory
into the kernel.
sparc64: I have no idea..
Drew
> slab_zalloc + 0xdf
> uma_zone_slab + 0xd8
> uma_zalloc_bucket + 0x15d
> uma_zalloc_arg + 0x307
> malloc
> ...
> m_getcl
>
> (gdb) l *slab_zalloc+0xdf
> 0xc02f646f is in slab_zalloc (../../../vm/uma_core.c:707).
> 702 else
> 703 wait &= ~M_ZERO;
> 704
> 705 if (booted || (zone->uz_flags & UMA_ZFLAG_PRIVALLOC)) {
> 706 mtx_lock(&Giant);
> 707 mem = zone->uz_allocf(zone,
> 708 zone->uz_ppera * UMA_SLAB_SIZE, &flags, wait);
> 709 mtx_unlock(&Giant);
> 710 if (mem == NULL) {
> 711 ZONE_LOCK(zone);
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