SMP linux help

sushil@iitk.ac.in ("sushil@iitk.ac.in")
Sat, 4 Sep 1999 17:55:38 +0530 (IST)

Hi,
I am running linux 2.9.9 kernel.
I am trying the understand the locking mechanism used in linux to make
the kernel SMP safe. In do_fork() (also in many other syscall interface
functions) there is call to lock_kernel() function. What does
lock_kernel() do? If it is used to synchronize the access to kernel data
structures from other processes on other processors, then why, after
having called this function, we again try to do some locking like calling
spin_lock(&lastpid_lock) in get_pid()?

I have seen the definition of lock_kernel. It increments the
current->lock_depth and if it nonzero then tries to lock the kernel_flag
variable.

Kindly reply.
I am on this mailing list.

Thanks,
Sushil.

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