[PATCH] f2fs: optimize fs_lock for better performance

[PATCH] f2fs: optimize fs_lock for better performance

[Chao Yu]

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Re: [PATCH] f2fs: optimize fs_lock for better performance

[Russ Knize]

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I encountered this same issue recently and solved it in much the same way.
 Can we rename "spin_lock" to something more meaningful?

This race actually exposed a potential deadlock between f2fs_create() and
f2fs_initxattrs():

- vfs_create()
 - f2fs_create() - takes an fs_lock
  - f2fs_add_link()
   - __f2fs_add_link()
    - init_inode_metadata()
     - f2fs_init_security()
      - security_inode_init_security()
       - f2fs_initxattrs()
        - f2fs_setxattr() - also takes an fs_lock

If another CPU happens to have the same lock that f2fs_setxattr() was
trying to take because of the race around next_lock_num, we can get into a
deadlock situation if the two threads are also contending over another
resource (like bdi).

Another scenario is if the above happens while another thread is in the
middle of grabbing all of the locks via mutex_lock_all().  f2fs_create() is
holding a lock that mutex_lock_all() is waiting for and mutex_lock_all() is
holding a lock that f2fs_setxattr() is waiting for.

Russ


On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <chao2.yu@samsung.com> wrote:

>  Hi Kim:****
>
> **     **I think there is a performance problem: when all sbi->fs_lock is
> holded,
>
> then all other threads may get the same next_lock value from
> sbi->next_lock_num in function mutex_lock_op,
>
> and wait to get the same lock at position fs_lock[next_lock], it unbalance
> the fs_lock usage.
>
> It may lost performance when we do the multithread test.****
>
> ** **
>
> Here is the patch to fix this problem:****
>
> ** **
>
> Signed-off-by: Yu Chao <chao2.yu@samsung.com>****
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h****
>
> old mode 100644****
>
> new mode 100755****
>
> index 467d42d..983bb45****
>
> --- a/fs/f2fs/f2fs.h****
>
> +++ b/fs/f2fs/f2fs.h****
>
> @@ -371,6 +371,7 @@ struct f2fs_sb_info {****
>
>         struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS operations
> */****
>
>         struct mutex node_write;                /* locking node writes */*
> ***
>
>         struct mutex writepages;                /* mutex for writepages()
> */****
>
> +       spinlock_t spin_lock;                   /* lock for next_lock_num
> */****
>
>         unsigned char next_lock_num;            /* round-robin global
> locks */****
>
>         int por_doing;                          /* recovery is doing or
> not */****
>
>         int on_build_free_nids;                 /* build_free_nids is
> doing */****
>
> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> f2fs_sb_info *sbi)****
>
>  ****
>
>  static inline int mutex_lock_op(struct f2fs_sb_info *sbi)****
>
>  {****
>
> -       unsigned char next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;***
> *
>
> +       unsigned char next_lock;****
>
>         int i = 0;****
>
>  ****
>
>         for (; i < NR_GLOBAL_LOCKS; i++)****
>
>                 if (mutex_trylock(&sbi->fs_lock[i]))****
>
>                         return i;****
>
>  ****
>
> -       mutex_lock(&sbi->fs_lock[next_lock]);****
>
> +       spin_lock(&sbi->spin_lock);****
>
> +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;****
>
>         sbi->next_lock_num++;****
>
> +       spin_unlock(&sbi->spin_lock);****
>
> +****
>
> +       mutex_lock(&sbi->fs_lock[next_lock]);****
>
>         return next_lock;****
>
>  }****
>
>  ****
>
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c****
>
> old mode 100644****
>
> new mode 100755****
>
> index 75c7dc3..4f27596****
>
> --- a/fs/f2fs/super.c****
>
> +++ b/fs/f2fs/super.c****
>
> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
> void *data, int silent)****
>
>         mutex_init(&sbi->cp_mutex);****
>
>         for (i = 0; i < NR_GLOBAL_LOCKS; i++)****
>
>                 mutex_init(&sbi->fs_lock[i]);****
>
> +       spin_lock_init(&sbi->spin_lock);****
>
>         mutex_init(&sbi->node_write);****
>
>         sbi->por_doing = 0;****
>
>         spin_lock_init(&sbi->stat_lock);****
>
> (END)****
>
> ** **
>
>
>
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Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better performance

[Jaegeuk Kim]

Hi,

At first, thank you for the report and please follow the email writing
rules. :)

Anyway, I agree to the below issue.
One thing that I can think of is that we don't need to use the
spin_lock, since we don't care about the exact lock number, but just
need to get any not-collided number.

So, how about removing the spin_lock?
And how about using a random number?
Thanks,

2013-09-06 (금), 09:48 +0000, Chao Yu:
> Hi Kim:
> 
>      I think there is a performance problem: when all sbi->fs_lock is
> holded, 
> 
> then all other threads may get the same next_lock value from
> sbi->next_lock_num in function mutex_lock_op, 
> 
> and wait to get the same lock at position fs_lock[next_lock], it
> unbalance the fs_lock usage. 
> 
> It may lost performance when we do the multithread test.
> 
>  
> 
> Here is the patch to fix this problem:
> 
>  
> 
> Signed-off-by: Yu Chao <chao2.yu@samsung.com>
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> 
> old mode 100644
> 
> new mode 100755
> 
> index 467d42d..983bb45
> 
> --- a/fs/f2fs/f2fs.h
> 
> +++ b/fs/f2fs/f2fs.h
> 
> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
> 
>         struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
> operations */
> 
>         struct mutex node_write;                /* locking node writes
> */
> 
>         struct mutex writepages;                /* mutex for
> writepages() */
> 
> +       spinlock_t spin_lock;                   /* lock for
> next_lock_num */
> 
>         unsigned char next_lock_num;            /* round-robin global
> locks */
> 
>         int por_doing;                          /* recovery is doing
> or not */
> 
>         int on_build_free_nids;                 /* build_free_nids is
> doing */
> 
> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> f2fs_sb_info *sbi)
> 
>  
> 
>  static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
> 
>  {
> 
> -       unsigned char next_lock = sbi->next_lock_num %
> NR_GLOBAL_LOCKS;
> 
> +       unsigned char next_lock;
> 
>         int i = 0;
> 
>  
> 
>         for (; i < NR_GLOBAL_LOCKS; i++)
> 
>                 if (mutex_trylock(&sbi->fs_lock[i]))
> 
>                         return i;
> 
>  
> 
> -       mutex_lock(&sbi->fs_lock[next_lock]);
> 
> +       spin_lock(&sbi->spin_lock);
> 
> +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
> 
>         sbi->next_lock_num++;
> 
> +       spin_unlock(&sbi->spin_lock);
> 
> +
> 
> +       mutex_lock(&sbi->fs_lock[next_lock]);
> 
>         return next_lock;
> 
>  }
> 
>  
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> 
> old mode 100644
> 
> new mode 100755
> 
> index 75c7dc3..4f27596
> 
> --- a/fs/f2fs/super.c
> 
> +++ b/fs/f2fs/super.c
> 
> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
> void *data, int silent)
> 
>         mutex_init(&sbi->cp_mutex);
> 
>         for (i = 0; i < NR_GLOBAL_LOCKS; i++)
> 
>                 mutex_init(&sbi->fs_lock[i]);
> 
> +       spin_lock_init(&sbi->spin_lock);
> 
>         mutex_init(&sbi->node_write);
> 
>         sbi->por_doing = 0;
> 
>         spin_lock_init(&sbi->stat_lock);
> 
> (END)
> 
>  
> 
> 
> 
> 

-- 
Jaegeuk Kim
Samsung

Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance

[Jaegeuk Kim]

Hi,

Nice catch.
This is definitely a bug where one thread grabbed two fs_locks across
the same flow.
Any idea?
Thanks,

2013-09-06 (금), 14:25 -0500, Russ Knize:
> I encountered this same issue recently and solved it in much the same
> way.  Can we rename "spin_lock" to something more meaningful?
> 
> 
> This race actually exposed a potential deadlock between f2fs_create()
> and f2fs_initxattrs():
> 
> 
> - vfs_create()
>  - f2fs_create() - takes an fs_lock
>   - f2fs_add_link()
>    - __f2fs_add_link()
>     - init_inode_metadata()
>      - f2fs_init_security()
>       - security_inode_init_security()
>        - f2fs_initxattrs()
>         - f2fs_setxattr() - also takes an fs_lock
> 
> 
> If another CPU happens to have the same lock that f2fs_setxattr() was
> trying to take because of the race around next_lock_num, we can get
> into a deadlock situation if the two threads are also contending over
> another resource (like bdi).
> 
> 
> Another scenario is if the above happens while another thread is in
> the middle of grabbing all of the locks via mutex_lock_all().
>  f2fs_create() is holding a lock that mutex_lock_all() is waiting for
> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
> for.
> 
> 
> Russ
> 
> 
> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <chao2.yu@samsung.com> wrote:
>         Hi Kim:
>         
>              I think there is a performance problem: when all
>         sbi->fs_lock is holded, 
>         
>         then all other threads may get the same next_lock value from
>         sbi->next_lock_num in function mutex_lock_op, 
>         
>         and wait to get the same lock at position fs_lock[next_lock],
>         it unbalance the fs_lock usage. 
>         
>         It may lost performance when we do the multithread test.
>         
>          
>         
>         Here is the patch to fix this problem:
>         
>          
>         
>         Signed-off-by: Yu Chao <chao2.yu@samsung.com>
>         
>         diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>         
>         old mode 100644
>         
>         new mode 100755
>         
>         index 467d42d..983bb45
>         
>         --- a/fs/f2fs/f2fs.h
>         
>         +++ b/fs/f2fs/f2fs.h
>         
>         @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>         
>                 struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
>         operations */
>         
>                 struct mutex node_write;                /* locking
>         node writes */
>         
>                 struct mutex writepages;                /* mutex for
>         writepages() */
>         
>         +       spinlock_t spin_lock;                   /* lock for
>         next_lock_num */
>         
>                 unsigned char next_lock_num;            /* round-robin
>         global locks */
>         
>                 int por_doing;                          /* recovery is
>         doing or not */
>         
>                 int on_build_free_nids;                 /*
>         build_free_nids is doing */
>         
>         @@ -533,15 +534,19 @@ static inline void
>         mutex_unlock_all(struct f2fs_sb_info *sbi)
>         
>          
>         
>          static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>         
>          {
>         
>         -       unsigned char next_lock = sbi->next_lock_num %
>         NR_GLOBAL_LOCKS;
>         
>         +       unsigned char next_lock;
>         
>                 int i = 0;
>         
>          
>         
>                 for (; i < NR_GLOBAL_LOCKS; i++)
>         
>                         if (mutex_trylock(&sbi->fs_lock[i]))
>         
>                                 return i;
>         
>          
>         
>         -       mutex_lock(&sbi->fs_lock[next_lock]);
>         
>         +       spin_lock(&sbi->spin_lock);
>         
>         +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>         
>                 sbi->next_lock_num++;
>         
>         +       spin_unlock(&sbi->spin_lock);
>         
>         +
>         
>         +       mutex_lock(&sbi->fs_lock[next_lock]);
>         
>                 return next_lock;
>         
>          }
>         
>          
>         
>         diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>         
>         old mode 100644
>         
>         new mode 100755
>         
>         index 75c7dc3..4f27596
>         
>         --- a/fs/f2fs/super.c
>         
>         +++ b/fs/f2fs/super.c
>         
>         @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct
>         super_block *sb, void *data, int silent)
>         
>                 mutex_init(&sbi->cp_mutex);
>         
>                 for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>         
>                         mutex_init(&sbi->fs_lock[i]);
>         
>         +       spin_lock_init(&sbi->spin_lock);
>         
>                 mutex_init(&sbi->node_write);
>         
>                 sbi->por_doing = 0;
>         
>                 spin_lock_init(&sbi->stat_lock);
>         
>         (END)
>         
>          
>         
>         
>         
>         
>         
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>         2012, more!
>         Discover the easy way to master current and previous Microsoft
>         technologies
>         and advance your career. Get an incredible 1,500+ hours of
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>         
> 
> 

-- 
Jaegeuk Kim
Samsung

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Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance

[Kim Jaegeuk]

Hi Russ,

The usage of fs_locks is for the recovery, so it doesn't matter
with stress-testing.
Actually what I've concerned is that we should not grab two or
more fs_locks in the same call path.
Thanks,

2013/9/11 Russ Knize <Russ.Knize@motorola.com>:
> Hi Jaegeuk/Gu,
>
> I've removed the lock and have been stress-testing with SELinux and some
> additional xattr torture for 24+ hours.  I have not encountered any issues
> yet.
>
> My previous suggestion about moving the lock is probably not a good idea
> without some significant code rework (thanks to the f2fs_balance_fs call in
> f2fs_setxattr).
>
> Russ
>
> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
>>
>> Hi Jaegeuk,
>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote:
>>
>> > Hi,
>> >
>> > 2013-09-07 (토), 08:00 +0000, Chao Yu:
>> >> Hi Knize,
>> >>
>> >>     Thanks for your reply, I think it's actually meaningless that it's
>> >> being named after "spin_lock",
>> >> it's better to rename this spinlock to "round_robin_lock".
>> >>
>> >>     This patch can only resolve the issue of unbalanced fs_lock usage,
>> >> it can not fix the deadlock issue.
>> >> can we fix deadlock issue through this method:
>> >>
>> >> - vfs_create()
>> >>  - f2fs_create() - takes an fs_lock and save current thread info into
>> >> thread_info[NR_GLOBAL_LOCKS]
>> >>   - f2fs_add_link()
>> >>    - __f2fs_add_link()
>> >>     - init_inode_metadata()
>> >>      - f2fs_init_security()
>> >>       - security_inode_init_security()
>> >>        - f2fs_initxattrs()
>> >>         - f2fs_setxattr() - get fs_lock only if there is no current
>> >> thread info in thread_info
>> >>
>> >> So it keeps one thread can only hold one fs_lock to avoid deadlock.
>> >> Can we use this solution?
>> >
>> > It could be.
>> > But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs()
>>
>> Agree. This fs_lock here is used to protect the xattr from parallel
>> modification,
>> but here is in the initxattrs routine, parallel modification can not
>> happen.
>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used
>> to
>> avoid parallel modification. So I think this fs_lock is needless.
>> Am I missing something?
>>
>> Regards,
>> Gu
>>
>> > level, since this case only happens when f2fs_initxattrs() is called.
>> > Let's think about ut in more detail.
>> > Thanks,
>> >
>> >>
>> >>
>> >>
>> >> thanks again!
>> >>
>> >>
>> >>
>> >> ------- Original Message -------
>> >>
>> >> Sender : Russ Knize<Russ.Knize@motorola.com>
>> >>
>> >> Date : 九月 07, 2013 04:25 (GMT+09:00)
>> >>
>> >> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better
>> >> performance
>> >>
>> >>
>> >>
>> >> I encountered this same issue recently and solved it in much the same
>> >> way.  Can we rename "spin_lock" to something more meaningful?
>> >>
>> >>
>> >> This race actually exposed a potential deadlock between f2fs_create()
>> >> and f2fs_initxattrs():
>> >>
>> >>
>> >> - vfs_create()
>> >>  - f2fs_create() - takes an fs_lock
>> >>   - f2fs_add_link()
>> >>    - __f2fs_add_link()
>> >>     - init_inode_metadata()
>> >>      - f2fs_init_security()
>> >>       - security_inode_init_security()
>> >>        - f2fs_initxattrs()
>> >>         - f2fs_setxattr() - also takes an fs_lock
>> >>
>> >>
>> >> If another CPU happens to have the same lock that f2fs_setxattr() was
>> >> trying to take because of the race around next_lock_num, we can get
>> >> into a deadlock situation if the two threads are also contending over
>> >> another resource (like bdi).
>> >>
>> >>
>> >> Another scenario is if the above happens while another thread is in
>> >> the middle of grabbing all of the locks via mutex_lock_all().
>> >>  f2fs_create() is holding a lock that mutex_lock_all() is waiting for
>> >> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
>> >> for.
>> >>
>> >>
>> >> Russ
>> >>
>> >>
>> >> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <chao2.yu@samsung.com> wrote:
>> >>         Hi Kim:
>> >>
>> >>              I think there is a performance problem: when all
>> >>         sbi->fs_lock is holded,
>> >>
>> >>         then all other threads may get the same next_lock value from
>> >>         sbi->next_lock_num in function mutex_lock_op,
>> >>
>> >>         and wait to get the same lock at position fs_lock[next_lock],
>> >>         it unbalance the fs_lock usage.
>> >>
>> >>         It may lost performance when we do the multithread test.
>> >>
>> >>
>> >>
>> >>         Here is the patch to fix this problem:
>> >>
>> >>
>> >>
>> >>         Signed-off-by: Yu Chao <chao2.yu@samsung.com>
>> >>
>> >>         diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> >>
>> >>         old mode 100644
>> >>
>> >>         new mode 100755
>> >>
>> >>         index 467d42d..983bb45
>> >>
>> >>         --- a/fs/f2fs/f2fs.h
>> >>
>> >>         +++ b/fs/f2fs/f2fs.h
>> >>
>> >>         @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>> >>
>> >>                 struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
>> >>         operations */
>> >>
>> >>                 struct mutex node_write;                /* locking
>> >>         node writes */
>> >>
>> >>                 struct mutex writepages;                /* mutex for
>> >>         writepages() */
>> >>
>> >>         +       spinlock_t spin_lock;                   /* lock for
>> >>         next_lock_num */
>> >>
>> >>                 unsigned char next_lock_num;            /* round-robin
>> >>         global locks */
>> >>
>> >>                 int por_doing;                          /* recovery is
>> >>         doing or not */
>> >>
>> >>                 int on_build_free_nids;                 /*
>> >>         build_free_nids is doing */
>> >>
>> >>         @@ -533,15 +534,19 @@ static inline void
>> >>         mutex_unlock_all(struct f2fs_sb_info *sbi)
>> >>
>> >>
>> >>
>> >>          static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>> >>
>> >>          {
>> >>
>> >>         -       unsigned char next_lock = sbi->next_lock_num %
>> >>         NR_GLOBAL_LOCKS;
>> >>
>> >>         +       unsigned char next_lock;
>> >>
>> >>                 int i = 0;
>> >>
>> >>
>> >>
>> >>                 for (; i < NR_GLOBAL_LOCKS; i++)
>> >>
>> >>                         if (mutex_trylock(&sbi->fs_lock[i]))
>> >>
>> >>                                 return i;
>> >>
>> >>
>> >>
>> >>         -       mutex_lock(&sbi->fs_lock[next_lock]);
>> >>
>> >>         +       spin_lock(&sbi->spin_lock);
>> >>
>> >>         +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>> >>
>> >>                 sbi->next_lock_num++;
>> >>
>> >>         +       spin_unlock(&sbi->spin_lock);
>> >>
>> >>         +
>> >>
>> >>         +       mutex_lock(&sbi->fs_lock[next_lock]);
>> >>
>> >>                 return next_lock;
>> >>
>> >>          }
>> >>
>> >>
>> >>
>> >>         diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>> >>
>> >>         old mode 100644
>> >>
>> >>         new mode 100755
>> >>
>> >>         index 75c7dc3..4f27596
>> >>
>> >>         --- a/fs/f2fs/super.c
>> >>
>> >>         +++ b/fs/f2fs/super.c
>> >>
>> >>         @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct
>> >>         super_block *sb, void *data, int silent)
>> >>
>> >>                 mutex_init(&sbi->cp_mutex);
>> >>
>> >>                 for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>> >>
>> >>                         mutex_init(&sbi->fs_lock[i]);
>> >>
>> >>         +       spin_lock_init(&sbi->spin_lock);
>> >>
>> >>                 mutex_init(&sbi->node_write);
>> >>
>> >>                 sbi->por_doing = 0;
>> >>
>> >>                 spin_lock_init(&sbi->stat_lock);
>> >>
>> >>         (END)
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> ------------------------------------------------------------------------------
>> >>         Learn the latest--Visual Studio 2012, SharePoint 2013, SQL
>> >>         2012, more!
>> >>         Discover the easy way to master current and previous Microsoft
>> >>         technologies
>> >>         and advance your career. Get an incredible 1,500+ hours of
>> >>         step-by-step
>> >>         tutorial videos with LearnDevNow. Subscribe today and save!
>> >>
>> >> http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk
>> >>         _______________________________________________
>> >>         Linux-f2fs-devel mailing list
>> >>         Linux-f2fs-devel@lists.sourceforge.net
>> >>         https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >
>>
>>
>
>
> ------------------------------------------------------------------------------
> How ServiceNow helps IT people transform IT departments:
> 1. Consolidate legacy IT systems to a single system of record for IT
> 2. Standardize and globalize service processes across IT
> 3. Implement zero-touch automation to replace manual, redundant tasks
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>

Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance

[Kim Jaegeuk]

Hi Gu,

2013/9/11 Gu Zheng <guz.fnst@cn.fujitsu.com>:
> Hi Jaegeuk, Chao,
>
> On 09/10/2013 08:52 AM, Jaegeuk Kim wrote:
>
>> Hi,
>>
>> At first, thank you for the report and please follow the email writing
>> rules. :)
>>
>> Anyway, I agree to the below issue.
>> One thing that I can think of is that we don't need to use the
>> spin_lock, since we don't care about the exact lock number, but just
>> need to get any not-collided number.
>
> IMHO, just moving sbi->next_lock_num++ before mutex_lock(&sbi->fs_lock[next_lock])
> can avoid unbalance issue mostly.
> IMO, the case two or more threads increase sbi->next_lock_num in the same time is
> really very very little. If you think it is not rigorous, change next_lock_num to
> atomic one can fix it.
> What's your opinion?

As your opinion, I think it is enough to replace it with simple
sbi->next_lock_num++.
Thanks,

>
> Regards,
> Gu
>
>>
>> So, how about removing the spin_lock?
>> And how about using a random number?
>
>> Thanks,
>>
>> 2013-09-06 (금), 09:48 +0000, Chao Yu:
>>> Hi Kim:
>>>
>>>      I think there is a performance problem: when all sbi->fs_lock is
>>> holded,
>>>
>>> then all other threads may get the same next_lock value from
>>> sbi->next_lock_num in function mutex_lock_op,
>>>
>>> and wait to get the same lock at position fs_lock[next_lock], it
>>> unbalance the fs_lock usage.
>>>
>>> It may lost performance when we do the multithread test.
>>>
>>>
>>>
>>> Here is the patch to fix this problem:
>>>
>>>
>>>
>>> Signed-off-by: Yu Chao <chao2.yu@samsung.com>
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>
>>> old mode 100644
>>>
>>> new mode 100755
>>>
>>> index 467d42d..983bb45
>>>
>>> --- a/fs/f2fs/f2fs.h
>>>
>>> +++ b/fs/f2fs/f2fs.h
>>>
>>> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>>>
>>>         struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
>>> operations */
>>>
>>>         struct mutex node_write;                /* locking node writes
>>> */
>>>
>>>         struct mutex writepages;                /* mutex for
>>> writepages() */
>>>
>>> +       spinlock_t spin_lock;                   /* lock for
>>> next_lock_num */
>>>
>>>         unsigned char next_lock_num;            /* round-robin global
>>> locks */
>>>
>>>         int por_doing;                          /* recovery is doing
>>> or not */
>>>
>>>         int on_build_free_nids;                 /* build_free_nids is
>>> doing */
>>>
>>> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
>>> f2fs_sb_info *sbi)
>>>
>>>
>>>
>>>  static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>>>
>>>  {
>>>
>>> -       unsigned char next_lock = sbi->next_lock_num %
>>> NR_GLOBAL_LOCKS;
>>>
>>> +       unsigned char next_lock;
>>>
>>>         int i = 0;
>>>
>>>
>>>
>>>         for (; i < NR_GLOBAL_LOCKS; i++)
>>>
>>>                 if (mutex_trylock(&sbi->fs_lock[i]))
>>>
>>>                         return i;
>>>
>>>
>>>
>>> -       mutex_lock(&sbi->fs_lock[next_lock]);
>>>
>>> +       spin_lock(&sbi->spin_lock);
>>>
>>> +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>>>
>>>         sbi->next_lock_num++;
>>>
>>> +       spin_unlock(&sbi->spin_lock);
>>>
>>> +
>>>
>>> +       mutex_lock(&sbi->fs_lock[next_lock]);
>>>
>>>         return next_lock;
>>>
>>>  }
>>>
>>>
>>>
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>
>>> old mode 100644
>>>
>>> new mode 100755
>>>
>>> index 75c7dc3..4f27596
>>>
>>> --- a/fs/f2fs/super.c
>>>
>>> +++ b/fs/f2fs/super.c
>>>
>>> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
>>> void *data, int silent)
>>>
>>>         mutex_init(&sbi->cp_mutex);
>>>
>>>         for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>>>
>>>                 mutex_init(&sbi->fs_lock[i]);
>>>
>>> +       spin_lock_init(&sbi->spin_lock);
>>>
>>>         mutex_init(&sbi->node_write);
>>>
>>>         sbi->por_doing = 0;
>>>
>>>         spin_lock_init(&sbi->stat_lock);
>>>
>>> (END)
>>>
>>>
>>>
>>>
>>>
>>>
>>
>
>
>
> ------------------------------------------------------------------------------
> How ServiceNow helps IT people transform IT departments:
> 1. Consolidate legacy IT systems to a single system of record for IT
> 2. Standardize and globalize service processes across IT
> 3. Implement zero-touch automation to replace manual, redundant tasks
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Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance

[Russ Knize]

Jaegeuk,

My tests include forced kernel panics while fsstress is running, which
generates a lot of recovery activity.  Sorry I wasn't more clear.

I understand your concern, which is why I first tried to keep the
fs_lock in the xattr_handler->set() path from VFS while removing it
from the call path I shared earlier.  Doing this requires reworking
the xattr code a bit.  Based on what Gu said about the inode mutex, it
seems like we can just remove it.

Russ

On Wed, Sep 11, 2013 at 8:19 AM, Kim Jaegeuk <jaegeuk.kim@gmail.com> wrote:
> Hi Russ,
>
> The usage of fs_locks is for the recovery, so it doesn't matter
> with stress-testing.
> Actually what I've concerned is that we should not grab two or
> more fs_locks in the same call path.
> Thanks,
>
> 2013/9/11 Russ Knize <Russ.Knize@motorola.com>:
>> Hi Jaegeuk/Gu,
>>
>> I've removed the lock and have been stress-testing with SELinux and some
>> additional xattr torture for 24+ hours.  I have not encountered any issues
>> yet.
>>
>> My previous suggestion about moving the lock is probably not a good idea
>> without some significant code rework (thanks to the f2fs_balance_fs call in
>> f2fs_setxattr).
>>
>> Russ
>>
>> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
>>>
>>> Hi Jaegeuk,
>>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote:
>>>
>>> > Hi,
>>> >
>>> > 2013-09-07 (토), 08:00 +0000, Chao Yu:
>>> >> Hi Knize,
>>> >>
>>> >>     Thanks for your reply, I think it's actually meaningless that it's
>>> >> being named after "spin_lock",
>>> >> it's better to rename this spinlock to "round_robin_lock".
>>> >>
>>> >>     This patch can only resolve the issue of unbalanced fs_lock usage,
>>> >> it can not fix the deadlock issue.
>>> >> can we fix deadlock issue through this method:
>>> >>
>>> >> - vfs_create()
>>> >>  - f2fs_create() - takes an fs_lock and save current thread info into
>>> >> thread_info[NR_GLOBAL_LOCKS]
>>> >>   - f2fs_add_link()
>>> >>    - __f2fs_add_link()
>>> >>     - init_inode_metadata()
>>> >>      - f2fs_init_security()
>>> >>       - security_inode_init_security()
>>> >>        - f2fs_initxattrs()
>>> >>         - f2fs_setxattr() - get fs_lock only if there is no current
>>> >> thread info in thread_info
>>> >>
>>> >> So it keeps one thread can only hold one fs_lock to avoid deadlock.
>>> >> Can we use this solution?
>>> >
>>> > It could be.
>>> > But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs()
>>>
>>> Agree. This fs_lock here is used to protect the xattr from parallel
>>> modification,
>>> but here is in the initxattrs routine, parallel modification can not
>>> happen.
>>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used
>>> to
>>> avoid parallel modification. So I think this fs_lock is needless.
>>> Am I missing something?
>>>
>>> Regards,
>>> Gu
>>>
>>> > level, since this case only happens when f2fs_initxattrs() is called.
>>> > Let's think about ut in more detail.
>>> > Thanks,
>>> >
>>> >>
>>> >>
>>> >>
>>> >> thanks again!
>>> >>
>>> >>
>>> >>
>>> >> ------- Original Message -------
>>> >>
>>> >> Sender : Russ Knize<Russ.Knize@motorola.com>
>>> >>
>>> >> Date : 九月 07, 2013 04:25 (GMT+09:00)
>>> >>
>>> >> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better
>>> >> performance
>>> >>
>>> >>
>>> >>
>>> >> I encountered this same issue recently and solved it in much the same
>>> >> way.  Can we rename "spin_lock" to something more meaningful?
>>> >>
>>> >>
>>> >> This race actually exposed a potential deadlock between f2fs_create()
>>> >> and f2fs_initxattrs():
>>> >>
>>> >>
>>> >> - vfs_create()
>>> >>  - f2fs_create() - takes an fs_lock
>>> >>   - f2fs_add_link()
>>> >>    - __f2fs_add_link()
>>> >>     - init_inode_metadata()
>>> >>      - f2fs_init_security()
>>> >>       - security_inode_init_security()
>>> >>        - f2fs_initxattrs()
>>> >>         - f2fs_setxattr() - also takes an fs_lock
>>> >>
>>> >>
>>> >> If another CPU happens to have the same lock that f2fs_setxattr() was
>>> >> trying to take because of the race around next_lock_num, we can get
>>> >> into a deadlock situation if the two threads are also contending over
>>> >> another resource (like bdi).
>>> >>
>>> >>
>>> >> Another scenario is if the above happens while another thread is in
>>> >> the middle of grabbing all of the locks via mutex_lock_all().
>>> >>  f2fs_create() is holding a lock that mutex_lock_all() is waiting for
>>> >> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
>>> >> for.
>>> >>
>>> >>
>>> >> Russ
>>> >>
>>> >>
>>> >> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <chao2.yu@samsung.com> wrote:
>>> >>         Hi Kim:
>>> >>
>>> >>              I think there is a performance problem: when all
>>> >>         sbi->fs_lock is holded,
>>> >>
>>> >>         then all other threads may get the same next_lock value from
>>> >>         sbi->next_lock_num in function mutex_lock_op,
>>> >>
>>> >>         and wait to get the same lock at position fs_lock[next_lock],
>>> >>         it unbalance the fs_lock usage.
>>> >>
>>> >>         It may lost performance when we do the multithread test.
>>> >>
>>> >>
>>> >>
>>> >>         Here is the patch to fix this problem:
>>> >>
>>> >>
>>> >>
>>> >>         Signed-off-by: Yu Chao <chao2.yu@samsung.com>
>>> >>
>>> >>         diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> >>
>>> >>         old mode 100644
>>> >>
>>> >>         new mode 100755
>>> >>
>>> >>         index 467d42d..983bb45
>>> >>
>>> >>         --- a/fs/f2fs/f2fs.h
>>> >>
>>> >>         +++ b/fs/f2fs/f2fs.h
>>> >>
>>> >>         @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>>> >>
>>> >>                 struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
>>> >>         operations */
>>> >>
>>> >>                 struct mutex node_write;                /* locking
>>> >>         node writes */
>>> >>
>>> >>                 struct mutex writepages;                /* mutex for
>>> >>         writepages() */
>>> >>
>>> >>         +       spinlock_t spin_lock;                   /* lock for
>>> >>         next_lock_num */
>>> >>
>>> >>                 unsigned char next_lock_num;            /* round-robin
>>> >>         global locks */
>>> >>
>>> >>                 int por_doing;                          /* recovery is
>>> >>         doing or not */
>>> >>
>>> >>                 int on_build_free_nids;                 /*
>>> >>         build_free_nids is doing */
>>> >>
>>> >>         @@ -533,15 +534,19 @@ static inline void
>>> >>         mutex_unlock_all(struct f2fs_sb_info *sbi)
>>> >>
>>> >>
>>> >>
>>> >>          static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>>> >>
>>> >>          {
>>> >>
>>> >>         -       unsigned char next_lock = sbi->next_lock_num %
>>> >>         NR_GLOBAL_LOCKS;
>>> >>
>>> >>         +       unsigned char next_lock;
>>> >>
>>> >>                 int i = 0;
>>> >>
>>> >>
>>> >>
>>> >>                 for (; i < NR_GLOBAL_LOCKS; i++)
>>> >>
>>> >>                         if (mutex_trylock(&sbi->fs_lock[i]))
>>> >>
>>> >>                                 return i;
>>> >>
>>> >>
>>> >>
>>> >>         -       mutex_lock(&sbi->fs_lock[next_lock]);
>>> >>
>>> >>         +       spin_lock(&sbi->spin_lock);
>>> >>
>>> >>         +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>>> >>
>>> >>                 sbi->next_lock_num++;
>>> >>
>>> >>         +       spin_unlock(&sbi->spin_lock);
>>> >>
>>> >>         +
>>> >>
>>> >>         +       mutex_lock(&sbi->fs_lock[next_lock]);
>>> >>
>>> >>                 return next_lock;
>>> >>
>>> >>          }
>>> >>
>>> >>
>>> >>
>>> >>         diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> >>
>>> >>         old mode 100644
>>> >>
>>> >>         new mode 100755
>>> >>
>>> >>         index 75c7dc3..4f27596
>>> >>
>>> >>         --- a/fs/f2fs/super.c
>>> >>
>>> >>         +++ b/fs/f2fs/super.c
>>> >>
>>> >>         @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct
>>> >>         super_block *sb, void *data, int silent)
>>> >>
>>> >>                 mutex_init(&sbi->cp_mutex);
>>> >>
>>> >>                 for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>>> >>
>>> >>                         mutex_init(&sbi->fs_lock[i]);
>>> >>
>>> >>         +       spin_lock_init(&sbi->spin_lock);
>>> >>
>>> >>                 mutex_init(&sbi->node_write);
>>> >>
>>> >>                 sbi->por_doing = 0;
>>> >>
>>> >>                 spin_lock_init(&sbi->stat_lock);
>>> >>
>>> >>         (END)
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >> ------------------------------------------------------------------------------
>>> >>         Learn the latest--Visual Studio 2012, SharePoint 2013, SQL
>>> >>         2012, more!
>>> >>         Discover the easy way to master current and previous Microsoft
>>> >>         technologies
>>> >>         and advance your career. Get an incredible 1,500+ hours of
>>> >>         step-by-step
>>> >>         tutorial videos with LearnDevNow. Subscribe today and save!
>>> >>
>>> >> http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk
>>> >>         _______________________________________________
>>> >>         Linux-f2fs-devel mailing list
>>> >>         Linux-f2fs-devel@lists.sourceforge.net
>>> >>         https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >
>>>
>>>
>>
>>
>> ------------------------------------------------------------------------------
>> How ServiceNow helps IT people transform IT departments:
>> 1. Consolidate legacy IT systems to a single system of record for IT
>> 2. Standardize and globalize service processes across IT
>> 3. Implement zero-touch automation to replace manual, redundant tasks
>> http://pubads.g.doubleclick.net/gampad/clk?id=51271111&iu=/4140/ostg.clktrk
>> _______________________________________________
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>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>
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Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance

[Jin Xu]

Hi,

On 11/09/2013 21:19, Kim Jaegeuk wrote:
> Hi Russ,
>
> The usage of fs_locks is for the recovery, so it doesn't matter
> with stress-testing.
> Actually what I've concerned is that we should not grab two or
> more fs_locks in the same call path.
> Thanks,
>

I am wondering why we don't use other kind of methods like r/w semaphore
instead of the fs_locks for access control purpose. Is it due to the
little lower performance of r/w semaphore or other reasons?

I think the r/w semaphore can bring more clearer access control over
the current fs_locks, and will not suffer the problems reported here.
It can be used in a way that i/o tasks just acquire read sem while the
checkpoint task takes the write sem.

Or do we have other better method?

Regards,
Jin

> 2013/9/11 Russ Knize <Russ.Knize@motorola.com>:
>> Hi Jaegeuk/Gu,
>>
>> I've removed the lock and have been stress-testing with SELinux and some
>> additional xattr torture for 24+ hours.  I have not encountered any issues
>> yet.
>>
>> My previous suggestion about moving the lock is probably not a good idea
>> without some significant code rework (thanks to the f2fs_balance_fs call in
>> f2fs_setxattr).
>>
>> Russ
>>
>> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
>>>
>>> Hi Jaegeuk,
>>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote:
>>>
>>>> Hi,
>>>>
>>>> 2013-09-07 (토), 08:00 +0000, Chao Yu:
>>>>> Hi Knize,
>>>>>
>>>>>      Thanks for your reply, I think it's actually meaningless that it's
>>>>> being named after "spin_lock",
>>>>> it's better to rename this spinlock to "round_robin_lock".
>>>>>
>>>>>      This patch can only resolve the issue of unbalanced fs_lock usage,
>>>>> it can not fix the deadlock issue.
>>>>> can we fix deadlock issue through this method:
>>>>>
>>>>> - vfs_create()
>>>>>   - f2fs_create() - takes an fs_lock and save current thread info into
>>>>> thread_info[NR_GLOBAL_LOCKS]
>>>>>    - f2fs_add_link()
>>>>>     - __f2fs_add_link()
>>>>>      - init_inode_metadata()
>>>>>       - f2fs_init_security()
>>>>>        - security_inode_init_security()
>>>>>         - f2fs_initxattrs()
>>>>>          - f2fs_setxattr() - get fs_lock only if there is no current
>>>>> thread info in thread_info
>>>>>
>>>>> So it keeps one thread can only hold one fs_lock to avoid deadlock.
>>>>> Can we use this solution?
>>>>
>>>> It could be.
>>>> But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs()
>>>
>>> Agree. This fs_lock here is used to protect the xattr from parallel
>>> modification,
>>> but here is in the initxattrs routine, parallel modification can not
>>> happen.
>>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used
>>> to
>>> avoid parallel modification. So I think this fs_lock is needless.
>>> Am I missing something?
>>>
>>> Regards,
>>> Gu
>>>
>>>> level, since this case only happens when f2fs_initxattrs() is called.
>>>> Let's think about ut in more detail.
>>>> Thanks,
>>>>
>>>>>
>>>>>
>>>>>
>>>>> thanks again!
>>>>>
>>>>>
>>>>>
>>>>> ------- Original Message -------
>>>>>
>>>>> Sender : Russ Knize<Russ.Knize@motorola.com>
>>>>>
>>>>> Date : 九月 07, 2013 04:25 (GMT+09:00)
>>>>>
>>>>> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better
>>>>> performance
>>>>>
>>>>>
>>>>>
>>>>> I encountered this same issue recently and solved it in much the same
>>>>> way.  Can we rename "spin_lock" to something more meaningful?
>>>>>
>>>>>
>>>>> This race actually exposed a potential deadlock between f2fs_create()
>>>>> and f2fs_initxattrs():
>>>>>
>>>>>
>>>>> - vfs_create()
>>>>>   - f2fs_create() - takes an fs_lock
>>>>>    - f2fs_add_link()
>>>>>     - __f2fs_add_link()
>>>>>      - init_inode_metadata()
>>>>>       - f2fs_init_security()
>>>>>        - security_inode_init_security()
>>>>>         - f2fs_initxattrs()
>>>>>          - f2fs_setxattr() - also takes an fs_lock
>>>>>
>>>>>
>>>>> If another CPU happens to have the same lock that f2fs_setxattr() was
>>>>> trying to take because of the race around next_lock_num, we can get
>>>>> into a deadlock situation if the two threads are also contending over
>>>>> another resource (like bdi).
>>>>>
>>>>>
>>>>> Another scenario is if the above happens while another thread is in
>>>>> the middle of grabbing all of the locks via mutex_lock_all().
>>>>>   f2fs_create() is holding a lock that mutex_lock_all() is waiting for
>>>>> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
>>>>> for.
>>>>>
>>>>>
>>>>> Russ
>>>>>
>>>>>
>>>>> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <chao2.yu@samsung.com> wrote:
>>>>>          Hi Kim:
>>>>>
>>>>>               I think there is a performance problem: when all
>>>>>          sbi->fs_lock is holded,
>>>>>
>>>>>          then all other threads may get the same next_lock value from
>>>>>          sbi->next_lock_num in function mutex_lock_op,
>>>>>
>>>>>          and wait to get the same lock at position fs_lock[next_lock],
>>>>>          it unbalance the fs_lock usage.
>>>>>
>>>>>          It may lost performance when we do the multithread test.
>>>>>
>>>>>
>>>>>
>>>>>          Here is the patch to fix this problem:
>>>>>
>>>>>
>>>>>
>>>>>          Signed-off-by: Yu Chao <chao2.yu@samsung.com>
>>>>>
>>>>>          diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>>
>>>>>          old mode 100644
>>>>>
>>>>>          new mode 100755
>>>>>
>>>>>          index 467d42d..983bb45
>>>>>
>>>>>          --- a/fs/f2fs/f2fs.h
>>>>>
>>>>>          +++ b/fs/f2fs/f2fs.h
>>>>>
>>>>>          @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>>>>>
>>>>>                  struct mutex fs_lock[NR_GLOBAL_LOCKS];  /* blocking FS
>>>>>          operations */
>>>>>
>>>>>                  struct mutex node_write;                /* locking
>>>>>          node writes */
>>>>>
>>>>>                  struct mutex writepages;                /* mutex for
>>>>>          writepages() */
>>>>>
>>>>>          +       spinlock_t spin_lock;                   /* lock for
>>>>>          next_lock_num */
>>>>>
>>>>>                  unsigned char next_lock_num;            /* round-robin
>>>>>          global locks */
>>>>>
>>>>>                  int por_doing;                          /* recovery is
>>>>>          doing or not */
>>>>>
>>>>>                  int on_build_free_nids;                 /*
>>>>>          build_free_nids is doing */
>>>>>
>>>>>          @@ -533,15 +534,19 @@ static inline void
>>>>>          mutex_unlock_all(struct f2fs_sb_info *sbi)
>>>>>
>>>>>
>>>>>
>>>>>           static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>>>>>
>>>>>           {
>>>>>
>>>>>          -       unsigned char next_lock = sbi->next_lock_num %
>>>>>          NR_GLOBAL_LOCKS;
>>>>>
>>>>>          +       unsigned char next_lock;
>>>>>
>>>>>                  int i = 0;
>>>>>
>>>>>
>>>>>
>>>>>                  for (; i < NR_GLOBAL_LOCKS; i++)
>>>>>
>>>>>                          if (mutex_trylock(&sbi->fs_lock[i]))
>>>>>
>>>>>                                  return i;
>>>>>
>>>>>
>>>>>
>>>>>          -       mutex_lock(&sbi->fs_lock[next_lock]);
>>>>>
>>>>>          +       spin_lock(&sbi->spin_lock);
>>>>>
>>>>>          +       next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>>>>>
>>>>>                  sbi->next_lock_num++;
>>>>>
>>>>>          +       spin_unlock(&sbi->spin_lock);
>>>>>
>>>>>          +
>>>>>
>>>>>          +       mutex_lock(&sbi->fs_lock[next_lock]);
>>>>>
>>>>>                  return next_lock;
>>>>>
>>>>>           }
>>>>>
>>>>>
>>>>>
>>>>>          diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>>>
>>>>>          old mode 100644
>>>>>
>>>>>          new mode 100755
>>>>>
>>>>>          index 75c7dc3..4f27596
>>>>>
>>>>>          --- a/fs/f2fs/super.c
>>>>>
>>>>>          +++ b/fs/f2fs/super.c
>>>>>
>>>>>          @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct
>>>>>          super_block *sb, void *data, int silent)
>>>>>
>>>>>                  mutex_init(&sbi->cp_mutex);
>>>>>
>>>>>                  for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>>>>>
>>>>>                          mutex_init(&sbi->fs_lock[i]);
>>>>>
>>>>>          +       spin_lock_init(&sbi->spin_lock);
>>>>>
>>>>>                  mutex_init(&sbi->node_write);
>>>>>
>>>>>                  sbi->por_doing = 0;
>>>>>
>>>>>                  spin_lock_init(&sbi->stat_lock);
>>>>>
>>>>>          (END)
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------------
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>>>>>
>>>>> http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk
>>>>>          _______________________________________________
>>>>>          Linux-f2fs-devel mailing list
>>>>>          Linux-f2fs-devel@lists.sourceforge.net
>>>>>          https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>>
>> ------------------------------------------------------------------------------
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>>
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