cgroup debug seems dead?

While running namespace checks to look for dead code, I found that debug_subsys is declared global but never used in current code.

This leads to the fact that since debug_subsys is never used, the whole set of debugging functions is also never used. Is the whole CGROUP_DEBUG config option dead?

Quoted 8 lines · Stephen Hemminger

While running namespace checks to look for dead code, I found that debug_subsys is declared global but never used in current code.

This leads to the fact that since debug_subsys is never used, the whole set of debugging functions is also never used. Is the whole CGROUP_DEBUG config option dead?

No, it's not.

The debug code has been moved from kernel/cgroup_debug.c to kernel/cgroup.c, but the config and the code is not dead.

Is it a false positive of that check? The pointer to debug_subsys is stored in an array, and the array will be iterated in some places, so debug_subsys will be accessed.

Where is it stored in an array?

~/kernel/linux-2.6$ git grep debug_subsys kernel/cgroup.c:        kfree(cont->subsys[debug_subsys_id]); kernel/cgroup.c:struct cgroup_subsys debug_subsys = { kernel/cgroup.c:        .subsys_id = debug_subsys_id,

Quoted 3 lines · Stephen Hemminger

Where is it stored in an array?

Quoted 4 lines

~/kernel/linux-2.6$ git grep debug_subsys kernel/cgroup.c:        kfree(cont->subsys[debug_subsys_id]); kernel/cgroup.c:struct cgroup_subsys debug_subsys = { kernel/cgroup.c:        .subsys_id = debug_subsys_id,

It's via the include of cgroup_subsys.h at the start of kernel/cgroup.c

Paul

That would work but doesn't because the following is missing in cgroup_subsys.h!

#ifdef CONFIG_CGROUP_DEBUG
SUBSYS(debug)
#endif

/* */

Quoted 8 lines · On Tue, 19 Oct 2010 18:14:10 -0700 Paul Menage…

Quoted 6 lines · Stephen Hemminger

Where is it stored in an array?

~/kernel/linux-2.6$ git grep debug_subsys
kernel/cgroup.c: kfree(cont->subsys[debug_subsys_id]);
kernel/cgroup.c:struct cgroup_subsys debug_subsys = {
kernel/cgroup.c: .subsys_id = debug_subsys_id,

Quoted 3 lines

It's via the include of cgroup_subsys.h at the start of kernel/cgroup.c

Paul

That would work but doesn't because the following is missing in cgroup_subsys.h!

#ifdef CONFIG_CGROUP_DEBUG
SUBSYS(debug)
#endif

Quoted 11 lines · Stephen Hemminger

Quoted 8 lines · On Tue, 19 Oct 2010 18:14:10 -0700 Paul Menage…

Quoted 6 lines · Stephen Hemminger

Where is it stored in an array?

~/kernel/linux-2.6$ git grep debug_subsys
kernel/cgroup.c: kfree(cont->subsys[debug_subsys_id]);
kernel/cgroup.c:struct cgroup_subsys debug_subsys = {
kernel/cgroup.c: .subsys_id = debug_subsys_id,

Quoted 6 lines

Quoted 3 lines

It's via the include of cgroup_subsys.h at the start of kernel/cgroup.c

Paul

That would work but doesn't because the following is missing in cgroup_subsys.h!

It's there in cgroup_subsys.h (2.6.36-rc8). What kernel are you using?

Quoted 12 lines · On Wed, 20 Oct 2010 09:43:06 +0800 Li Zefan…

Quoted 11 lines · Stephen Hemminger

Quoted 8 lines · On Tue, 19 Oct 2010 18:14:10 -0700 Paul Menage…

Quoted 6 lines · Stephen Hemminger

Where is it stored in an array?

~/kernel/linux-2.6$ git grep debug_subsys
kernel/cgroup.c: kfree(cont->subsys[debug_subsys_id]);
kernel/cgroup.c:struct cgroup_subsys debug_subsys = {
kernel/cgroup.c: .subsys_id = debug_subsys_id,

Quoted 6 lines

Quoted 5 lines

Quoted 3 lines

It's via the include of cgroup_subsys.h at the start of kernel/cgroup.c

Paul

That would work but doesn't because the following is missing in cgroup_subsys.h!

It's there in cgroup_subsys.h (2.6.36-rc8). What kernel are you using?

Found it, thanks. Still not sure why the tools were confused.

Quoted 22 lines · Stephen Hemminger

Quoted 18 lines · On Wed, 20 Oct 2010 09:43:06 +0800 Li Zefan…

Quoted 11 lines · Stephen Hemminger

Quoted 8 lines · On Tue, 19 Oct 2010 18:14:10 -0700 Paul Menage…

Quoted 6 lines · Stephen Hemminger

Where is it stored in an array?

~/kernel/linux-2.6$ git grep debug_subsys
kernel/cgroup.c: kfree(cont->subsys[debug_subsys_id]);
kernel/cgroup.c:struct cgroup_subsys debug_subsys = {
kernel/cgroup.c: .subsys_id = debug_subsys_id,

Quoted 5 lines

Quoted 3 lines

It's via the include of cgroup_subsys.h at the start of kernel/cgroup.c

Paul

That would work but doesn't because the following is missing in cgroup_subsys.h!

It's there in cgroup_subsys.h (2.6.36-rc8). What kernel are you using?

Quoted 2 lines

Found it, thanks. Still not sure why the tools were confused.

That's normal. Think about how many false positives we can get with checkpatch.pl.

Your tools should be static code analyzers, and the macro we use in cgroup is too complex for them.