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userspace: allow thread IDs to be re-used

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It's currently too easy to run out of thread IDs as they
are never re-used on thread exit.

Now the kernel maintains a bitfield of in-use thread IDs,
updated on thread creation and termination. When a thread
exits, the permission bitfield for all kernel objects is
updated to revoke access for that retired thread ID, so that
a new thread re-using that ID will not gain access to objects
that it should not have.

Because of these runtime updates, setting the permission
bitmap for an object to all ones for a "public" object doesn't
work properly any more; a flag is now set for this instead.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-10-13 13:57:07 -07:00 • committed by Andrew Boie
commit 04caa679c9
7 changed files with 97 additions and 20 deletions
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5
kernel/include/kernel_structs.h
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@ -118,6 +118,11 @@ struct _kernel {
struct k_thread *threads; /* singly linked list of ALL fiber+tasks */
#endif
#if defined(CONFIG_USERSPACE)
/* 0 bits for ids currently in use, 1 for free ids */
u8_t free_thread_ids[CONFIG_MAX_THREAD_BYTES];
#endif
/* arch-specific part of _kernel */
struct _kernel_arch arch;
};