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In arch/ia64/kernel/ptrace.c there is a test for a peek or poke of a register image (in register backing storage). The test can be unnecessarily long (and occurs while holding the tasklist_lock). Especially long on a large system with thousands of active tasks. The ptrace caller (presumably a debugger) specifies the pid of its target and an address to peek or poke. But the debugger could be attached to several tasks. The idea of find_thread_for_addr() is to find whether the target address is in the RBS for any of those tasks. Currently it searches the thread-list of the target pid. If that search does not find a match, and the shared mm-struct's user count indicates that there are other tasks sharing this address space (a rare occurrence), a search is made of all the tasks in the system. Another approach can drastically shorten this procedure. It depends upon the fact that in order to peek or poke from/to any task, the debugger must first attach to that task. And when it does, the attached task is made a child of the debugger (is chained to its children list). Therefore we can search just the debugger's children list. Signed-off-by: Cliff Wickman <cpw@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com> |
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