linux-kernel - Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

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Date:	Mon, 15 Jun 2009 10:18:31 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Pekka J Enberg <penberg@...helsinki.fi>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, cl@...ux-foundation.org,
	kamezawa.hiroyu@...fujitsu.com, lizf@...fujitsu.com, mingo@...e.hu,
	npiggin@...e.de, yinghai@...nel.org, benh@...nel.crashing.org
Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

On Fri, Jun 12, 2009 at 07:16:30PM +0300, Pekka J Enberg wrote:
> Hi Linus,
> 
> I dropped the GFP_WAIT conversion patch and added the gfp masking patch 
> you liked. I tested this on x86-64 with both SLAB and SLUB.

Hi Pekka,

I tried to convert some of the early allocations on s390. Some callsites
however need to have the GFP_DMA flag, since we need to allocate memory below
2GB. Passing GFP_DMA causes this crash:

    <1>Unable to handle kernel pointer dereference at virtual kernel address fffffffffffff000
    <4>Oops: 0038 [#1] PREEMPT SMP 
    <4>Modules linked in:
    <4>CPU: 0 Not tainted 2.6.30-03984-g45e3e19-dirty #233
    <4>Process swapper (pid: 0, task: 00000000006a2ef0, ksp: 0000000000718000)
    <4>Krnl PSW : 0700100180000000 00000000000808ee (queue_work_on+0x8e/0xe0)
    <4>           R:0 T:1 IO:1 EX:1 Key:0 M:0 W:0 P:0 AS:0 CC:1 PM:0 EA:3
    <4>Krnl GPRS: 0000000000000000 ffffffffffffffff 0000000000000000 00000000006b8b88
    <4>           00000000006b8b88 0000000000000001 0000000000000008 0000000000000200
    <4>           000000003fe28000 0000000000008001 00000000011da730 0000000000717ca0
    <4>           00000000006b8b88 0000000000488650 0000000000717cd0 0000000000717ca0
    <4>Krnl Code: 00000000000808de: e310d0000082        xg      %r1,0(%r13)
    <4>           00000000000808e4: eb220003000d        sllg    %r2,%r2,3
    <4>           00000000000808ea: b9040034            lgr     %r3,%r4
    <4>          >00000000000808ee: e32210000004        lg      %r2,0(%r2,%r1)
    <4>           00000000000808f4: c0e5ffffff28        brasl   %r14,80744
    <4>           00000000000808fa: a7280001            lhi     %r2,1
    <4>           00000000000808fe: e340b0b80004        lg      %r4,184(%r11)
    <4>           0000000000080904: b9140022            lgfr    %r2,%r2
    <4>Call Trace:
    <4>([<000000003fe28000>] 0x3fe28000)
    <4> [<0000000000080e96>] queue_work+0x62/0xa4
    <4> [<0000000000080f26>] schedule_work+0x4e/0x60
    <4> [<0000000000132f7e>] dma_kmalloc_cache+0x1ca/0x1d0
    <4> [<00000000001330ae>] get_slab+0x12a/0x130
    <4> [<00000000001337b6>] __kmalloc+0x5e/0x364
    <4> [<0000000000739132>] con3215_init+0x1c2/0x2e4
    <4> [<00000000007333ea>] console_init+0x42/0x5c
    <4> [<0000000000718e50>] start_kernel+0x53c/0x6b8
    <4> [<0000000000012020>] _ehead+0x20/0x80

I didn't look any deeper into this, but looks to me like doing something like
schedule_work() this early isn't ok.

This is the conversion that leads to the crash:

-               alloc_bootmem_low(sizeof(struct raw3215_info));
+               kzalloc(sizeof(struct raw3215_info), GFP_NOWAIT | GFP_DMA);

Might be that I missed something. Maybe some special flag?
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