Add: tasklist_lock

[jqwang1992]

For_each_process() were called many times by other function of linux kernel and tasklist is often modifed, so we need lock to protect the tasklist. Tasklist_lock is the special lock to protect tasklist in linux kernel.

[wangxiaoq]

OK, I will merge it after test

[wangxiaoq]

When I compile it I got the following warning, please make sure you have test it before issue a PR.

make -C /lib/modules/uname -r/build M=/home/wangxq/dump-phys-addr modules
make[1]: Entering directory `/usr/src/linux-headers-4.4.0-31-generic'
CC [M] /home/wangxq/dump-phys-addr/dump-phys.o
Building modules, stage 2.
MODPOST 1 modules
**

WARNING: "tasklist_lock" [/home/wangxq/dump-phys-addr/dump-phys.ko] undefined!

**
CC /home/wangxq/dump-phys-addr/dump-phys.mod.o
LD [M] /home/wangxq/dump-phys-addr/dump-phys.ko
make[1]: Leaving directory `/usr/src/linux-headers-4.4.0-31-generic'

[jqwang1992]

Yes, I did, but it's need to EXPORT_SYMBOL(tasklist_lock). Here's why:

-What: remove EXPORT_SYMBOL(tasklist_lock)
-When: August 2006
-Files: kernel/fork.c
-Why: tasklist_lock protects the kernel internal task list. Modules have
no business looking at it, and all instances in drivers have been due
to use of too-lowlevel APIs. Having this symbol exported prevents
moving to more scalable locking schemes for the task list.
-Who: Christoph Hellwig hch@lst.de

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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.4.89&id=c59923a15c12d2b3597af913bf234a0ef264a38b