what is spinlock depth

what is spinlock depth

[Sri Ram Vemulpali]

Hi all,

I am reading spinlock code and looking at struct raw_spinlock. I found
struct lockdep_map as member.
which is defined as

struct lockdep_map {
       struct lock_class_key           *key;
       struct lock_class               *class_cache[NR_LOCKDEP_CACHING_CLASSES];
       const char                      *name;
#ifdef CONFIG_LOCK_STAT
       int                             cpu;
      unsigned long                   ip;
#endif
};

Can anyone help me explain, how this struct helps the spinlock. Why do
we need lockdepth.
Thanks for help in advance.
-- 
Regards,
Sri.

Re: what is spinlock depth

[Jiri Slaby]

On 01/31/2011 09:27 PM, Sri Ram Vemulpali wrote:
> Hi all,
> 
> I am reading spinlock code and looking at struct raw_spinlock. I found
> struct lockdep_map as member.
> which is defined as
> 
> struct lockdep_map {
>        struct lock_class_key           *key;
>        struct lock_class               *class_cache[NR_LOCKDEP_CACHING_CLASSES];
>        const char                      *name;
> #ifdef CONFIG_LOCK_STAT
>        int                             cpu;
>       unsigned long                   ip;
> #endif
> };
> 
> Can anyone help me explain, how this struct helps the spinlock. Why do
> we need lockdepth.

It's not dep-th, but dep-endency. It's a debugging technique to
dynamically check for locking correctness. See more details in
Documentation/lockdep-design.txt.

-- 
js

Re: what is spinlock depth

[Rajat Sharma]

lockdep finds out dependency in locking order at runtime. More on this
in kernel documentation linux/Documentation/lockdep-design.txt

Rajat

On Tue, Feb 1, 2011 at 1:57 AM, Sri Ram Vemulpali
<sri.ram.gmu06@gmail.com> wrote:
> Hi all,
>
> I am reading spinlock code and looking at struct raw_spinlock. I found
> struct lockdep_map as member.
> which is defined as
>
> struct lockdep_map {
>       struct lock_class_key           *key;
>       struct lock_class               *class_cache[NR_LOCKDEP_CACHING_CLASSES];
>       const char                      *name;
> #ifdef CONFIG_LOCK_STAT
>       int                             cpu;
>      unsigned long                   ip;
> #endif
> };
>
> Can anyone help me explain, how this struct helps the spinlock. Why do
> we need lockdepth.
> Thanks for help in advance.
> --
> Regards,
> Sri.
>
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> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
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>

Re: what is spinlock depth

[WANG Cong]

On Mon, 31 Jan 2011 15:27:08 -0500, Sri Ram Vemulpali wrote:

> Hi all,
> 
> I am reading spinlock code and looking at struct raw_spinlock. I found
> struct lockdep_map as member.
...
> Can anyone help me explain, how this struct helps the spinlock. Why do
> we need lockdepth.

Here "lockdep" is short for Lock Dependence, not Lock Depth.

We do have lock depth things, e.g. ->lock_depth of struct task_struct,
which means the nested level of BKL. But spinlock can't be nested.