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SubjectRe: get_task_struct()
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On Sat, 2004-04-17 at 12:46 -0300, Fabiano Ramos wrote:

> Inside sys_ptrace, the function get_task_struct is invoked after
> retrieving the child's task srtuct pointer. Why is it done? I have
> tracked down the code and noticed that it is in fact an increment
> on the (page?) counter. Can you help me understand it?

Think of get_task_struct(foo) as a reference count on foo's task
structure. So long as the reference count is elevated, foo's task
structure cannot be deallocated.

get_task_struct() is called here because sys_ptrace() needs to ensure
that the child's task structure does not go away out from under this
function, but we do not want to hold the tasklist_lock.

> Is it necessary to call free_task_struct whenever its get counterpart
> is called?

Yes, although it is called "put_task_struct()". It is called at the end
of this function.

Robert Love


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