Messages in this thread Patch in this message | | | Date | Thu, 29 Nov 2007 15:32:18 -0600 | From | Matt Mackall <> | Subject | Re: [bug] SLOB, tipc_init(), WARNING: at arch/x86/mm/highmem_32.c:52 kmap_atomic_prot() |
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On Thu, Nov 29, 2007 at 03:39:20PM +0100, Ingo Molnar wrote: > > * Ingo Molnar <mingo@elte.hu> wrote: > > > i'm getting this on 32-bit (with the kmap-atomic debugging patch > > applied): > > > > ----------------> > > Calling initcall 0x78b67c00: tipc_init+0x0/0xc0() > > TIPC: Activated (version 1.6.2 compiled Nov 29 2007 15:04:36) > > WARNING: at arch/x86/mm/highmem_32.c:52 kmap_atomic_prot() > > Pid: 1, comm: swapper Not tainted 2.6.24-rc3-cfs-v24 #45 > > [<78107272>] show_trace_log_lvl+0x12/0x40 > > [<781072ad>] show_trace+0xd/0x20 > > [<781086f8>] dump_stack+0x58/0x60 > > [<7811541f>] kmap_atomic_prot+0x1bf/0x240 > > [<781154ae>] kmap_atomic+0xe/0x20 > > [<78157be5>] get_page_from_freelist+0x225/0x420 > > [<78157e4d>] __alloc_pages+0x6d/0x3a0 > > [<78169a7b>] slob_new_page+0x1b/0x60 > > [<78169be4>] slob_alloc+0x124/0x1e0 > > [<78169e0f>] __kmalloc_node+0x6f/0xa0 > > [<7884f7c2>] reg_init+0x42/0x80 > > [<7884f80a>] tipc_reg_start+0xa/0x40 > > [<7883e6c6>] tipc_core_start+0x66/0xc0 > > [<78b67c81>] tipc_init+0x81/0xc0 > > this is due to the kzalloc() here: > > 0x7884f1d0 is in reg_init (net/tipc/user_reg.c:88). > 83 spin_lock_bh(®_lock); > 84 if (!users) { > 85 users = kzalloc(USER_LIST_SIZE, GFP_ATOMIC); > 86 if (users) { > 87 for (i = 1; i <= MAX_USERID; i++) { > 88 users[i].next = i - 1; > > which does a: > > 120 static inline void clear_highpage(struct page *page) > 121 { > 122 void *kaddr = kmap_atomic(page, KM_USER0); > 123 clear_page(kaddr); > 124 kunmap_atomic(kaddr, KM_USER0); > 125 } > > but ... why does the debug code think it's in softirq context? > > plus, and this is a slob question i guess, how come we drop into > clear_highpage() for a kzalloc()??
Good question. Looks like kzalloc switched from doing a memset to passing a GFP_ZERO flag down to kmalloc. Slob didn't get completely updated to reflect this, so it blindly propagates the flag onto __alloc_pages and does a harmless double-clear.
Someone should remind us what the point of moving the kzalloc memset down into the allocators was. We now have all three allocators doing:
if (unlikely((flags & __GFP_ZERO) && ptr)) memset(ptr, 0, obj_size(cachep));
and needing to mask flags before passing them to page allocators, which hardly seems better than kzalloc unconditionally doing the memset. Wouldn't it be better/faster/smaller to make kzalloc a non-inline?
Slob also has a nice second path for large kmallocs where it just calls the page allocator directly which also needs this treatment. Which does the right thing with non-highmem systems, but can hit this bug otherwise.
Below is a totally untested patch. Alternately, we could simply tweak clear_highpage to remove the limitation, but that would leave slob doing an extra clear.
diff -r c60016ba6237 mm/slob.c --- a/mm/slob.c Tue Nov 13 09:09:36 2007 -0800 +++ b/mm/slob.c Thu Nov 29 15:15:54 2007 -0600 @@ -223,6 +231,7 @@ static void *slob_new_page(gfp_t gfp, in { void *page; + gfp &= ~__GFP_ZERO; #ifdef CONFIG_NUMA if (node != -1) page = alloc_pages_node(node, gfp, order); @@ -457,6 +470,8 @@ void *__kmalloc_node(size_t size, gfp_t page = virt_to_page(ret); page->private = size; } + if (unlikely((gfp & __GFP_ZERO) && ret)) + memset(ret, 0, size); return ret; } } -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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