Patchwork x86, alternative: fix p6 nops on non-modular kernels

login
register
mail settings
Submitter Avi Kivity
Date Aug. 22, 2012, 10:03 a.m.
Message ID <5034AE84.90708@redhat.com>
Download mbox | patch
Permalink /patch/179280/
State New
Headers show

Comments

Avi Kivity - Aug. 22, 2012, 10:03 a.m.
On 08/22/2012 12:54 PM, Avi Kivity wrote:
> On 08/21/2012 12:28 PM, Tomas Racek wrote:
>> 
>> http://fi.muni.cz/~xracek/debian2.img.bz2
>> 
>> Other things are the same.
>> 
>> The runtest.sh sets environment for xfstests and runs test 285 which I wrote and and which should test if FS sends discard requests only on free sectors:
>> 285:
>> 1. Create loop device and FS on it.
>> 2. Populate it with some garbage.
>> 3. Get free sectors from FS.
>> 4. Run fstrim and look for discard requests via blk tracer.
>> 5. Compare free sectors to discard requests.
>> 
>> The test itself can have some issues but I'm pretty sure it shouldn't crash the system. ;-)
> 
> Does the following patch help?
> 

It's obvious that it should.  You're running a non-modular kernel, and those nops are discarded (probably a leftover from the days patching was a boot-only activity), so the kernel patched garbage over its own code.

-------8<----cut-here-----8<-----------------------------------

From: Avi Kivity <avi@redhat.com>
Date: Wed, 22 Aug 2012 12:58:18 +0300
Subject: [PATCH] x86, alternative: fix p6 nops on non-modular kernels

Probably a leftover from the early days of self-patching, p6nops are
marked __initconst_or_module, which causes them to be discarded in a
non-modular kernel.  If something later triggers patching, it will
overwrite kernel code with garbage.

Reported-by: Tomas Racek <tracek@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Tomas Racek - Aug. 22, 2012, 10:33 a.m.
----- Original Message -----
> On 08/22/2012 12:54 PM, Avi Kivity wrote:
> > On 08/21/2012 12:28 PM, Tomas Racek wrote:
> >> 
> >> http://fi.muni.cz/~xracek/debian2.img.bz2
> >> 
> >> Other things are the same.
> >> 
> >> The runtest.sh sets environment for xfstests and runs test 285
> >> which I wrote and and which should test if FS sends discard
> >> requests only on free sectors:
> >> 285:
> >> 1. Create loop device and FS on it.
> >> 2. Populate it with some garbage.
> >> 3. Get free sectors from FS.
> >> 4. Run fstrim and look for discard requests via blk tracer.
> >> 5. Compare free sectors to discard requests.
> >> 
> >> The test itself can have some issues but I'm pretty sure it
> >> shouldn't crash the system. ;-)
> > 
> > Does the following patch help?
> > 
> 
> It's obvious that it should.  You're running a non-modular kernel,
> and those nops are discarded (probably a leftover from the days
> patching was a boot-only activity), so the kernel patched garbage
> over its own code.
> 

Works fine. Thank you!

Tom


> -------8<----cut-here-----8<-----------------------------------
> 
> From: Avi Kivity <avi@redhat.com>
> Date: Wed, 22 Aug 2012 12:58:18 +0300
> Subject: [PATCH] x86, alternative: fix p6 nops on non-modular kernels
> 
> Probably a leftover from the early days of self-patching, p6nops are
> marked __initconst_or_module, which causes them to be discarded in a
> non-modular kernel.  If something later triggers patching, it will
> overwrite kernel code with garbage.
> 
> Reported-by: Tomas Racek <tracek@redhat.com>
> Signed-off-by: Avi Kivity <avi@redhat.com>
> 
> diff --git a/arch/x86/kernel/alternative.c
> b/arch/x86/kernel/alternative.c
> index afb7ff7..ced4534 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -165,7 +165,7 @@ static int __init setup_noreplace_paravirt(char
> *str)
>  #endif
>  
>  #ifdef P6_NOP1
> -static const unsigned char  __initconst_or_module p6nops[] =
> +static const unsigned char p6nops[] =
>  {
>  	P6_NOP1,
>  	P6_NOP2,
> 
> 
> --
> error compiling committee.c: too many arguments to function
>

Patch

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index afb7ff7..ced4534 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -165,7 +165,7 @@  static int __init setup_noreplace_paravirt(char *str)
 #endif
 
 #ifdef P6_NOP1
-static const unsigned char  __initconst_or_module p6nops[] =
+static const unsigned char p6nops[] =
 {
 	P6_NOP1,
 	P6_NOP2,