Messages in this thread |  | | Date | Sat, 23 Dec 2000 14:05:37 +0000 (GMT) | From | Tigran Aivazian <> | Subject | Re: why both kernel lock as well as semaphore |
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On Sat, 23 Dec 2000, Sourav Sen wrote:
> > In many parts of the kernel, I have seen both semaphore is taken > (eg. down(¤t->mm->mmap_sem)) as well as kernel lock (lock_kernel()) > is also taken, why both are required? Whats the purpose of each? >
because the semaphore is really needed (by design of the subsystem) but the big kernel lock (BKL) is taken "just in case", i.e. just in case the design is broken. Occasionally, the lock is removed to "see what happens" -- if nobody complains then the design is probably correct i.e. things are declared to "just work" and the attention is shifted to some other subsystem.... :)
Does it make things clearer?
Regards, Tigran
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