linux-kernel - Re: [bug] SLOB, tipc_init(), WARNING: at arch/x86/mm/highmem_32.c:52 kmap_atomic

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Date:	Thu, 29 Nov 2007 15:39:20 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Allan Stephens <allan.stephens@...driver.com>,
	Jon Paul Maloy <jon.maloy@...csson.com>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [bug] SLOB, tipc_init(), WARNING: at
	arch/x86/mm/highmem_32.c:52 kmap_atomic_prot()


* Ingo Molnar <mingo@...e.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(&reg_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()??

	Ingo
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