linux-kernel - Re: [PATCH, REGRESSION v3] mm: make apply_to_page

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Message-ID: <alpine.DEB.2.10.1601211511230.9813@chino.kir.corp.google.com>
Date:	Thu, 21 Jan 2016 15:12:44 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Mika Penttilä <mika.penttila@...tfour.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH, REGRESSION v3] mm: make apply_to_page_range more
 robust

On Thu, 21 Jan 2016, Mika Penttilä wrote:

> Recent changes (4.4.0+) in module loader triggered oops on ARM : 
> 
> The module in question is in-tree module :
> drivers/misc/ti-st/st_drv.ko
> 
> The BUG is here :
> 
> [ 53.638335] ------------[ cut here ]------------
> [ 53.642967] kernel BUG at mm/memory.c:1878!
> [ 53.647153] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
> [ 53.652987] Modules linked in:
> [ 53.656061] CPU: 0 PID: 483 Comm: insmod Not tainted 4.4.0 #3
> [ 53.661808] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> [ 53.668338] task: a989d400 ti: 9e6a2000 task.ti: 9e6a2000
> [ 53.673751] PC is at apply_to_page_range+0x204/0x224
> [ 53.678723] LR is at change_memory_common+0x90/0xdc
> [ 53.683604] pc : [<800ca0ec>] lr : [<8001d668>] psr: 600b0013
> [ 53.683604] sp : 9e6a3e38 ip : 8001d6b4 fp : 7f0042fc
> [ 53.695082] r10: 00000000 r9 : 9e6a3e90 r8 : 00000080
> [ 53.700309] r7 : 00000000 r6 : 7f008000 r5 : 7f008000 r4 : 7f008000
> [ 53.706837] r3 : 8001d5a4 r2 : 7f008000 r1 : 7f008000 r0 : 80b8d3c0
> [ 53.713368] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> [ 53.720504] Control: 10c5387d Table: 2e6b804a DAC: 00000055
> [ 53.726252] Process insmod (pid: 483, stack limit = 0x9e6a2210)
> [ 53.732173] Stack: (0x9e6a3e38 to 0x9e6a4000)
> [ 53.736532] 3e20: 7f007fff 7f008000
> [ 53.744714] 3e40: 80b8d3c0 80b8d3c0 00000000 7f007000 7f00426c 7f008000 00000000 7f008000
> [ 53.752895] 3e60: 7f004140 7f008000 00000000 00000080 00000000 00000000 7f0042fc 8001d668
> [ 53.761076] 3e80: 9e6a3e90 00000000 8001d6b4 7f00426c 00000080 00000000 9e6a3f58 7f004140
> [ 53.769257] 3ea0: 7f004240 7f00414c 00000000 8008bbe0 00000000 7f000000 00000000 00000000
> [ 53.777438] 3ec0: a8b12f00 0001cfd4 7f004250 7f004240 80b8159c 00000000 000000e0 7f0042fc
> [ 53.785619] 3ee0: c183d000 000074f8 000018fd 00000000 0b30000c 00000000 00000000 7f002024
> [ 53.793800] 3f00: 00000002 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [ 53.801980] 3f20: 00000000 00000000 00000000 00000000 00000040 00000000 00000003 0001cfd4
> [ 53.810161] 3f40: 0000017b 8000f7e4 9e6a2000 00000000 00000002 8008c498 c183d000 000074f8
> [ 53.818342] 3f60: c1841588 c1841409 c1842950 00005000 000052a0 00000000 00000000 00000000
> [ 53.826523] 3f80: 00000023 00000024 0000001a 0000001e 00000016 00000000 00000000 00000000
> [ 53.834703] 3fa0: 003e3d60 8000f640 00000000 00000000 00000003 0001cfd4 00000000 003e3d60
> [ 53.842884] 3fc0: 00000000 00000000 003e3d60 0000017b 003e3d20 7eabc9d4 76f2c000 00000002
> [ 53.851065] 3fe0: 7eabc990 7eabc980 00016320 76e81d00 600b0010 00000003 00000000 00000000
> [ 53.859256] [<800ca0ec>] (apply_to_page_range) from [<8001d668>] (change_memory_common+0x90/0xdc)
> [ 53.868139] [<8001d668>] (change_memory_common) from [<8008bbe0>] (load_module+0x194c/0x2068)
> [ 53.876671] [<8008bbe0>] (load_module) from [<8008c498>] (SyS_finit_module+0x64/0x74)
> [ 53.884512] [<8008c498>] (SyS_finit_module) from [<8000f640>] (ret_fast_syscall+0x0/0x34)
> [ 53.892694] Code: e0834104 eaffffbc e51a1008 eaffffac (e7f001f2)
> [ 53.898792] ---[ end trace fe43fc78ebde29a3 ]---
> 

NACK to your patch as it is just covering up buggy code silently.  The 
problem needs to be addressed in change_memory_common() to return if there 
is no size to change (numpages == 0).  It's a two line fix to that 
function.