Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Miao Xie 
On Fri, 30 Jan 2015 09:33:17 +0800, Qu Wenruo wrote:
 
  Original Message 
 Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse 
 mount
 option in a atomic way
 From: Miao Xie miao...@huawei.com
 To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
 Date: 2015年01月30日 09:29
 On Fri, 30 Jan 2015 09:20:46 +0800, Qu Wenruo wrote:
 Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
 info-mount_opt instead of new_opt.
 Thanks for pointing out this one.
 But I worried that this is not key reason of the wrong space cache. Could
 you explain the race condition which caused the wrong space cache?

 Thanks
 Miao
 CPU0:
 remount()
 |- sync_fs() - after sync_fs() we can start new trans
 |- btrfs_parse_options() CPU1:
  |- start_transaction()
  |- Do some bg allocation, not recorded in space_cache.
 I think it is a bug if a free space is not recorded in space cache. Could you
 explain why it is not recorded?

 Thanks
 Miao
 IIRC, in that window, the fs_info-mount_opt's SPACE_CACHE bit is cleared.
 So space cache is not recorded.

SPACE_CACHE is used to control cache write out, not in-memory cache. All the
free space should be recorded in in-memory cache.And when we write out
the in-memory space cache, we need protect the space cache from changing.

Thanks
Miao

 
 Thanks,
 Qu

   |- set SPACE_CACHE bit due to cache_gen

  |- commit_transaction()
  |- write space cache and update cache_gen.
  but since some of it is not recorded in space
 cache,
  the space cache missing some records.
   |- clear SPACE_CACHE bit dut to nospace_cache

 So the space cache is wrong.

 Thanks,
 Qu
 +}
kfree(orig);
return ret;
}

 .

 
 

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Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Miao Xie 
On Thu, 29 Jan 2015 10:24:35 +0800, Qu Wenruo wrote:
 Current btrfs_parse_options() is not atomic, which can set and clear a
 bit, especially for nospace_cache case.
 
 For example, if a fs is mounted with nospace_cache,
 btrfs_parse_options() will set SPACE_CACHE bit first(since
 cache_generation is non-zeo) and clear the SPACE_CACHE bit due to
 nospace_cache mount option.
 So under heavy operations and remount a nospace_cache btrfs, there is a
 windows for commit to create space cache.
 
 This bug can be reproduced by fstest/btrfs/071 073 074 with
 nospace_cache mount option. It has about 50% chance to create space
 cache, and about 10% chance to create wrong space cache, which can't
 pass btrfsck.
 
 This patch will do the mount option parse in a copy-and-update method.
 First copy the mount_opt from fs_info to new_opt, and only update
 options in new_opt. At last, copy the new_opt back to
 fs_info-mount_opt.
 
 This patch is already good enough to fix the above nospace_cache +
 remount bug, but need later patch to make sure mount options does not
 change during transaction.
 
 Signed-off-by: Qu Wenruo quwen...@cn.fujitsu.com
 ---
  fs/btrfs/ctree.h |  16 
  fs/btrfs/super.c | 115 
 +--
  2 files changed, 69 insertions(+), 62 deletions(-)
 
 diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
 index 5f99743..26bb47b 100644
 --- a/fs/btrfs/ctree.h
 +++ b/fs/btrfs/ctree.h
 @@ -2119,18 +2119,18 @@ struct btrfs_ioctl_defrag_range_args {
  #define btrfs_test_opt(root, opt)((root)-fs_info-mount_opt  \
BTRFS_MOUNT_##opt)
  
 -#define btrfs_set_and_info(root, opt, fmt, args...)  \
 +#define btrfs_set_and_info(fs_info, val, opt, fmt, args...)  \
  {\
 - if (!btrfs_test_opt(root, opt)) \
 - btrfs_info(root-fs_info, fmt, ##args); \
 - btrfs_set_opt(root-fs_info-mount_opt, opt);   \
 + if (!btrfs_raw_test_opt(val, opt))  \
 + btrfs_info(fs_info, fmt, ##args);   \
 + btrfs_set_opt(val, opt);\
  }
  
 -#define btrfs_clear_and_info(root, opt, fmt, args...)
 \
 +#define btrfs_clear_and_info(fs_info, val, opt, fmt, args...)
 \
  {\
 - if (btrfs_test_opt(root, opt))  \
 - btrfs_info(root-fs_info, fmt, ##args); \
 - btrfs_clear_opt(root-fs_info-mount_opt, opt); \
 + if (btrfs_raw_test_opt(val, opt))   \
 + btrfs_info(fs_info, fmt, ##args);   \
 + btrfs_clear_opt(val, opt);  \
  }
  
  /*
 diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
 index b0c45b2..490fe1f 100644
 --- a/fs/btrfs/super.c
 +++ b/fs/btrfs/super.c
 @@ -395,10 +395,13 @@ int btrfs_parse_options(struct btrfs_root *root, char 
 *options)
   int ret = 0;
   char *compress_type;
   bool compress_force = false;
 + unsigned long new_opt;
 +
 + new_opt = info-mount_opt;

Here and

  
   cache_gen = btrfs_super_cache_generation(root-fs_info-super_copy);
   if (cache_gen)
 - btrfs_set_opt(info-mount_opt, SPACE_CACHE);
[SNIP]
  out:
 - if (!ret  btrfs_test_opt(root, SPACE_CACHE))
 - btrfs_info(root-fs_info, disk space caching is enabled);
 + if (!ret) {
 + if (btrfs_raw_test_opt(new_opt, SPACE_CACHE))
 + btrfs_info(info, disk space caching is enabled);
 + info-mount_opt = new_opt;

Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
info-mount_opt instead of new_opt.

But I worried that this is not key reason of the wrong space cache. Could
you explain the race condition which caused the wrong space cache?

Thanks
Miao

 + }
   kfree(orig);
   return ret;
  }
 

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Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Qu Wenruo 


 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() 
parse mount option in a atomic way

From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 08:31

On Thu, 29 Jan 2015 10:24:35 +0800, Qu Wenruo wrote:

Current btrfs_parse_options() is not atomic, which can set and clear a
bit, especially for nospace_cache case.

For example, if a fs is mounted with nospace_cache,
btrfs_parse_options() will set SPACE_CACHE bit first(since
cache_generation is non-zeo) and clear the SPACE_CACHE bit due to
nospace_cache mount option.
So under heavy operations and remount a nospace_cache btrfs, there is a
windows for commit to create space cache.

This bug can be reproduced by fstest/btrfs/071 073 074 with
nospace_cache mount option. It has about 50% chance to create space
cache, and about 10% chance to create wrong space cache, which can't
pass btrfsck.

This patch will do the mount option parse in a copy-and-update method.
First copy the mount_opt from fs_info to new_opt, and only update
options in new_opt. At last, copy the new_opt back to
fs_info-mount_opt.

This patch is already good enough to fix the above nospace_cache +
remount bug, but need later patch to make sure mount options does not
change during transaction.

Signed-off-by: Qu Wenruo quwen...@cn.fujitsu.com
---
  fs/btrfs/ctree.h |  16 
  fs/btrfs/super.c | 115 +--
  2 files changed, 69 insertions(+), 62 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5f99743..26bb47b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2119,18 +2119,18 @@ struct btrfs_ioctl_defrag_range_args {
  #define btrfs_test_opt(root, opt) ((root)-fs_info-mount_opt  \
 BTRFS_MOUNT_##opt)
  
-#define btrfs_set_and_info(root, opt, fmt, args...)			\

+#define btrfs_set_and_info(fs_info, val, opt, fmt, args...)\
  { \
-   if (!btrfs_test_opt(root, opt)) \
-   btrfs_info(root-fs_info, fmt, ##args);  \
-   btrfs_set_opt(root-fs_info-mount_opt, opt); \
+   if (!btrfs_raw_test_opt(val, opt))  \
+   btrfs_info(fs_info, fmt, ##args);   \
+   btrfs_set_opt(val, opt);\
  }
  
-#define btrfs_clear_and_info(root, opt, fmt, args...)			\

+#define btrfs_clear_and_info(fs_info, val, opt, fmt, args...)  \
  { \
-   if (btrfs_test_opt(root, opt))  \
-   btrfs_info(root-fs_info, fmt, ##args);  \
-   btrfs_clear_opt(root-fs_info-mount_opt, opt);   \
+   if (btrfs_raw_test_opt(val, opt))   \
+   btrfs_info(fs_info, fmt, ##args);   \
+   btrfs_clear_opt(val, opt);  \
  }
  
  /*

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index b0c45b2..490fe1f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -395,10 +395,13 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
int ret = 0;
char *compress_type;
bool compress_force = false;
+   unsigned long new_opt;
+
+   new_opt = info-mount_opt;

Here and

  
  	cache_gen = btrfs_super_cache_generation(root-fs_info-super_copy);

if (cache_gen)
-   btrfs_set_opt(info-mount_opt, SPACE_CACHE);

[SNIP]

  out:
-   if (!ret  btrfs_test_opt(root, SPACE_CACHE))
-   btrfs_info(root-fs_info, disk space caching is enabled);
+   if (!ret) {
+   if (btrfs_raw_test_opt(new_opt, SPACE_CACHE))
+   btrfs_info(info, disk space caching is enabled);
+   info-mount_opt = new_opt;

Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
info-mount_opt instead of new_opt.

Thanks for pointing out this one.


But I worried that this is not key reason of the wrong space cache. Could
you explain the race condition which caused the wrong space cache?

Thanks
Miao

CPU0:
remount()
|- sync_fs() - after sync_fs() we can start new trans
|- btrfs_parse_options() CPU1:
|- start_transaction()
|- Do some bg allocation, not recorded in space_cache.
 |- set SPACE_CACHE bit due to cache_gen

|- commit_transaction()
|- write space cache and update cache_gen.
but since some of it is not recorded in 
space cache,

the space cache missing some records.
 |- clear SPACE_CACHE bit dut to nospace_cache

So the space cache is wrong

Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Qu Wenruo 


 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() 
parse mount option in a atomic way

From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 09:29

On Fri, 30 Jan 2015 09:20:46 +0800, Qu Wenruo wrote:

Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
info-mount_opt instead of new_opt.

Thanks for pointing out this one.

But I worried that this is not key reason of the wrong space cache. Could
you explain the race condition which caused the wrong space cache?

Thanks
Miao

CPU0:
remount()
|- sync_fs() - after sync_fs() we can start new trans
|- btrfs_parse_options() CPU1:
 |- start_transaction()
 |- Do some bg allocation, not recorded in space_cache.

I think it is a bug if a free space is not recorded in space cache. Could you
explain why it is not recorded?

Thanks
Miao

IIRC, in that window, the fs_info-mount_opt's SPACE_CACHE bit is cleared.
So space cache is not recorded.

Thanks,
Qu



  |- set SPACE_CACHE bit due to cache_gen

 |- commit_transaction()
 |- write space cache and update cache_gen.
 but since some of it is not recorded in space 
cache,
 the space cache missing some records.
  |- clear SPACE_CACHE bit dut to nospace_cache

So the space cache is wrong.

Thanks,
Qu

+}
   kfree(orig);
   return ret;
   }


.



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Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Qu Wenruo 


 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() 
parse mount option in a atomic way

From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 10:06

On Fri, 30 Jan 2015 09:33:17 +0800, Qu Wenruo wrote:

 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount
option in a atomic way
From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 09:29

On Fri, 30 Jan 2015 09:20:46 +0800, Qu Wenruo wrote:

Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
info-mount_opt instead of new_opt.

Thanks for pointing out this one.

But I worried that this is not key reason of the wrong space cache. Could
you explain the race condition which caused the wrong space cache?

Thanks
Miao

CPU0:
remount()
|- sync_fs() - after sync_fs() we can start new trans
|- btrfs_parse_options() CPU1:
  |- start_transaction()
  |- Do some bg allocation, not recorded in space_cache.

I think it is a bug if a free space is not recorded in space cache. Could you
explain why it is not recorded?

Thanks
Miao

IIRC, in that window, the fs_info-mount_opt's SPACE_CACHE bit is cleared.
So space cache is not recorded.

SPACE_CACHE is used to control cache write out, not in-memory cache. All the
free space should be recorded in in-memory cache.And when we write out
the in-memory space cache, we need protect the space cache from changing.

Thanks
Miao
You're right, the wrong space cache problem is not caused by the 
non-atomic mount option problem.
But the atomic mount option change with per-transaction mount option 
will at least make it disappear

when using nospace_cache mount option.

Thanks,
Qu



Thanks,
Qu

   |- set SPACE_CACHE bit due to cache_gen

  |- commit_transaction()
  |- write space cache and update cache_gen.
  but since some of it is not recorded in space
cache,
  the space cache missing some records.
   |- clear SPACE_CACHE bit dut to nospace_cache

So the space cache is wrong.

Thanks,
Qu

+}
kfree(orig);
return ret;
}


.





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Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Miao Xie 
On Fri, 30 Jan 2015 10:51:52 +0800, Qu Wenruo wrote:
 
  Original Message 
 Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse 
 mount
 option in a atomic way
 From: Miao Xie miao...@huawei.com
 To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
 Date: 2015年01月30日 10:06
 On Fri, 30 Jan 2015 09:33:17 +0800, Qu Wenruo wrote:
  Original Message 
 Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse 
 mount
 option in a atomic way
 From: Miao Xie miao...@huawei.com
 To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
 Date: 2015年01月30日 09:29
 On Fri, 30 Jan 2015 09:20:46 +0800, Qu Wenruo wrote:
 Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
 info-mount_opt instead of new_opt.
 Thanks for pointing out this one.
 But I worried that this is not key reason of the wrong space cache. Could
 you explain the race condition which caused the wrong space cache?

 Thanks
 Miao
 CPU0:
 remount()
 |- sync_fs() - after sync_fs() we can start new trans
 |- btrfs_parse_options() CPU1:
   |- start_transaction()
   |- Do some bg allocation, not recorded in 
 space_cache.
 I think it is a bug if a free space is not recorded in space cache. Could 
 you
 explain why it is not recorded?

 Thanks
 Miao
 IIRC, in that window, the fs_info-mount_opt's SPACE_CACHE bit is cleared.
 So space cache is not recorded.
 SPACE_CACHE is used to control cache write out, not in-memory cache. All the
 free space should be recorded in in-memory cache.And when we write out
 the in-memory space cache, we need protect the space cache from changing.

 Thanks
 Miao
 You're right, the wrong space cache problem is not caused by the non-atomic
 mount option problem.
 But the atomic mount option change with per-transaction mount option will at
 least make it disappear
 when using nospace_cache mount option.

But we need fix a problem, not hide a problem.

Thanks
Miao

 
 Thanks,
 Qu

 Thanks,
 Qu
|- set SPACE_CACHE bit due to cache_gen

   |- commit_transaction()
   |- write space cache and update cache_gen.
   but since some of it is not recorded in 
 space
 cache,
   the space cache missing some records.
|- clear SPACE_CACHE bit dut to nospace_cache

 So the space cache is wrong.

 Thanks,
 Qu
 +}
 kfree(orig);
 return ret;
 }

 .


 
 .
 

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Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-29 Thread Qu Wenruo 


 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() 
parse mount option in a atomic way

From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 11:21

On Fri, 30 Jan 2015 10:51:52 +0800, Qu Wenruo wrote:

 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount
option in a atomic way
From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 10:06

On Fri, 30 Jan 2015 09:33:17 +0800, Qu Wenruo wrote:

 Original Message 
Subject: Re: [PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount
option in a atomic way
From: Miao Xie miao...@huawei.com
To: Qu Wenruo quwen...@cn.fujitsu.com, linux-btrfs@vger.kernel.org
Date: 2015年01月30日 09:29

On Fri, 30 Jan 2015 09:20:46 +0800, Qu Wenruo wrote:

Here need ACCESS_ONCE to wrap info-mount_opt, or the complier might use
info-mount_opt instead of new_opt.

Thanks for pointing out this one.

But I worried that this is not key reason of the wrong space cache. Could
you explain the race condition which caused the wrong space cache?

Thanks
Miao

CPU0:
remount()
|- sync_fs() - after sync_fs() we can start new trans
|- btrfs_parse_options() CPU1:
   |- start_transaction()
   |- Do some bg allocation, not recorded in space_cache.

I think it is a bug if a free space is not recorded in space cache. Could you
explain why it is not recorded?

Thanks
Miao

IIRC, in that window, the fs_info-mount_opt's SPACE_CACHE bit is cleared.
So space cache is not recorded.

SPACE_CACHE is used to control cache write out, not in-memory cache. All the
free space should be recorded in in-memory cache.And when we write out
the in-memory space cache, we need protect the space cache from changing.

Thanks
Miao

You're right, the wrong space cache problem is not caused by the non-atomic
mount option problem.
But the atomic mount option change with per-transaction mount option will at
least make it disappear
when using nospace_cache mount option.

But we need fix a problem, not hide a problem.

Thanks
Miao

Yes, But I don't mean to hide it.
If it's a bug in space cache, it will still be reproducible on with 
space_cache mount option.


The patch itself is focused on the space cache created with 
nospace_cache mount option,

at least it's doing it job.

The wrong space cahce problem is another story then.
I'll remove the wrong space cache description in the commit message in 
next version.


Thanks,
Qu



Thanks,
Qu

Thanks,
Qu

|- set SPACE_CACHE bit due to cache_gen

   |- commit_transaction()
   |- write space cache and update cache_gen.
   but since some of it is not recorded in space
cache,
   the space cache missing some records.
|- clear SPACE_CACHE bit dut to nospace_cache

So the space cache is wrong.

Thanks,
Qu

+}
 kfree(orig);
 return ret;
 }


.


.



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[PATCH RESEND v4 2/8] btrfs: Make btrfs_parse_options() parse mount option in a atomic way

2015-01-28 Thread Qu Wenruo 
Current btrfs_parse_options() is not atomic, which can set and clear a
bit, especially for nospace_cache case.

For example, if a fs is mounted with nospace_cache,
btrfs_parse_options() will set SPACE_CACHE bit first(since
cache_generation is non-zeo) and clear the SPACE_CACHE bit due to
nospace_cache mount option.
So under heavy operations and remount a nospace_cache btrfs, there is a
windows for commit to create space cache.

This bug can be reproduced by fstest/btrfs/071 073 074 with
nospace_cache mount option. It has about 50% chance to create space
cache, and about 10% chance to create wrong space cache, which can't
pass btrfsck.

This patch will do the mount option parse in a copy-and-update method.
First copy the mount_opt from fs_info to new_opt, and only update
options in new_opt. At last, copy the new_opt back to
fs_info-mount_opt.

This patch is already good enough to fix the above nospace_cache +
remount bug, but need later patch to make sure mount options does not
change during transaction.

Signed-off-by: Qu Wenruo quwen...@cn.fujitsu.com
---
 fs/btrfs/ctree.h |  16 
 fs/btrfs/super.c | 115 +--
 2 files changed, 69 insertions(+), 62 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5f99743..26bb47b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2119,18 +2119,18 @@ struct btrfs_ioctl_defrag_range_args {
 #define btrfs_test_opt(root, opt)  ((root)-fs_info-mount_opt  \
 BTRFS_MOUNT_##opt)
 
-#define btrfs_set_and_info(root, opt, fmt, args...)\
+#define btrfs_set_and_info(fs_info, val, opt, fmt, args...)\
 {  \
-   if (!btrfs_test_opt(root, opt)) \
-   btrfs_info(root-fs_info, fmt, ##args); \
-   btrfs_set_opt(root-fs_info-mount_opt, opt);   \
+   if (!btrfs_raw_test_opt(val, opt))  \
+   btrfs_info(fs_info, fmt, ##args);   \
+   btrfs_set_opt(val, opt);\
 }
 
-#define btrfs_clear_and_info(root, opt, fmt, args...)  \
+#define btrfs_clear_and_info(fs_info, val, opt, fmt, args...)  \
 {  \
-   if (btrfs_test_opt(root, opt))  \
-   btrfs_info(root-fs_info, fmt, ##args); \
-   btrfs_clear_opt(root-fs_info-mount_opt, opt); \
+   if (btrfs_raw_test_opt(val, opt))   \
+   btrfs_info(fs_info, fmt, ##args);   \
+   btrfs_clear_opt(val, opt);  \
 }
 
 /*
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index b0c45b2..490fe1f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -395,10 +395,13 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
int ret = 0;
char *compress_type;
bool compress_force = false;
+   unsigned long new_opt;
+
+   new_opt = info-mount_opt;
 
cache_gen = btrfs_super_cache_generation(root-fs_info-super_copy);
if (cache_gen)
-   btrfs_set_opt(info-mount_opt, SPACE_CACHE);
+   btrfs_set_opt(new_opt, SPACE_CACHE);
 
if (!options)
goto out;
@@ -422,7 +425,7 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
switch (token) {
case Opt_degraded:
btrfs_info(root-fs_info, allowing degraded mounts);
-   btrfs_set_opt(info-mount_opt, DEGRADED);
+   btrfs_set_opt(new_opt, DEGRADED);
break;
case Opt_subvol:
case Opt_subvolid:
@@ -434,7 +437,7 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
 */
break;
case Opt_nodatasum:
-   btrfs_set_and_info(root, NODATASUM,
+   btrfs_set_and_info(info, new_opt, NODATASUM,
   setting nodatasum);
break;
case Opt_datasum:
@@ -444,8 +447,8 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
else
btrfs_info(root-fs_info, setting 
datasum);
}
-   btrfs_clear_opt(info-mount_opt, NODATACOW);
-   btrfs_clear_opt(info-mount_opt, NODATASUM);
+   btrfs_clear_opt(new_opt, NODATACOW);
+   btrfs_clear_opt(new_opt, NODATASUM);
break;
case Opt_nodatacow:
if