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Memory Management for S elf-Stabilizing O perating S ystems

Memory Management for S elf-Stabilizing O perating S ystems. Shlomi Dolev and Reuven Yagel Computer Science Department Ben-Gurion University of the Negev, Beer-Sheva, Israel. SSS’05. SOS - Motivation. Growing interest in self-* / autonomic computing systems

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Memory Management for S elf-Stabilizing O perating S ystems

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  1. Memory Management forSelf-Stabilizing Operating Systems Shlomi Dolev and Reuven Yagel Computer Science Department Ben-Gurion University of the Negev, Beer-Sheva, Israel SSS’05

  2. SOS - Motivation • Growing interest in self-* / autonomic computing systems • Self-stabilizing algorithms/programs assume hardware and operating system are also stabilizing • Pentium HALTING problem: “… if the ESP or SP register is 1 when the PUSH instruction is executed, the processor shuts down…”

  3. Proposed solution • To build according to the well defined and understood paradigm of self-stabilization (traditionally used in distributed systems) • Thereby achieving: trustworthiness, dependability, self-healing, automatic recovery, adaptive systems, …

  4. OS Reliability • Past examples: • Dijkstra, “THE” Multiprogramming System ’68 (Layered Approach) • Denning, Fault tolerant operating systems ’76 (Protection) • KeyKOS ‘85, EROS ’92 (Capabilities, Checkpoints) • Micro-kernel ~‘90, Exo-kernel ’94 (Minimal TCB) • Current • JHU: The Coyotos Secure Operating System • IBM: K42, Autonomic Computing • SUN: Solaris 10, Predictive Self-Healing • MSR: Singularity, managed code OS

  5. A problem has been detected and Windows has been shut down to prevent damage to your computer. PFN_LIST_CORRUPT If this is the first time you've seen this error screen, restart your computer. If this screen appears again, follow these steps: Check to make sure any new hardware or software is properly installed. If this is a new installation, ask your hardware or software manufacturer for any Windows updates you might need. If problems continue, disable or remove any newly installed hardware or software. Disable BIOS memory options such as caching or shadowing. If you need to use Safe Mode to remove or disable components, restart your computer, press F8 to select Advanced Startup Options, and then select Safe Mode. Technical information: *** STOP: 0x0000004e (0x00000099, 0x00000000, 0x00000000, 0x00000000) Beginning dump of physical memory Physical memory dump complete. Contact your system administrator or technical support group for further assistance.

  6. Goal: Autonomic Computer • Following any sequence of transient faults (e.g. soft-errors), the (operating) system converges • Using self stabilization: • A system can be started in an arbitrary state and converge to a desired behavior • Using fair composition to run hardware+OS • BGU: Self-stabilizing systems, tools & paradigms • Microprocessor [DH’04] • Operating System [DY’04] • Compiler [DH’05] • Framework: autonomic recoverer [BDK’03] • Middleware: File System [DK’02], Group Comm. [DS’01]

  7. SOS - Directions • Black-box • Take existing (Desktop/Real-time) OS • Add stabilization layer • Detailed formal specification needed • Carefully tailoring a tiny kernel • Processor scheduling [SAACS04] • Memory management [SSS05] • Device drivers

  8. Method • Additional requirements for each OS function • Evolve self-stabilizing solutions that follow computer-architecture/OS progress • Detailed proof for self-stabilization of algorithms AND implementation • Processor (e.g. Pentium) instruction manual defines a transition function • Don’t rely on existing compilers

  9. Assumptions • Whole soft-state can be corrupted (e.g. Program Counter) • Stabilization of other layers

  10. Solution Foundations • Program loading & process scheduling • Code portions in ROM • Truly non-maskable interrupt and watchdog architecture • Periodic reset reinstall & execute (weak) • continuous monitoring and consistency enforcement

  11. Memory Management: Requirements • Consistency of memory hierarchy • Self-stabilization preservation

  12. Solution 1: Full Swapping • Allocate whole available memory to the running application • Consistency: kept all the time • Stabil. Preserving: no mutual sharing App1 App2 OS RAM App1 App2 App3 App … Disk

  13. Solution 2: Fixed Partitioning • Fixed slots in main memory for several programs c5 d5 c2 d2 OS RAM c1 c2 c3 c3 c4 c5 CD-ROM Disk d1 d2 d3 d3 d4 d5

  14. # F R P1 2 4 P2 -1 3 ... # P F1 F2 1 … Solution 2: Fixed Partitioning Process Table • Consistency: through continuous checks and consistency establishmentof OS data structures • Stabil. Preserving: via segmentation + code refreshing Frame Table

  15. Solution 3: Dynamic allocations • We want to allow applications to dynamically allocate memory • How can we avoid a process that (faultily) allocates the whole available memory? • What happens if a process “forgets” about its ownership? • Leasing

  16. # F R P1 -1 2 -1 P2 -1 1 -1 ... 2 1 -1 1 L 1 9 3 2 0 Request Queue 3 0 1 2 0 Solution 3: Dynamic allocations Process Table • Consistency: dynamic memory is temporarily leased & garbage collected, verification of PCB & queue • Stabil. Preserving: access through special segment selector # P P2 F1 Frame Table F2 …

  17. Implementation • Pentium in real-mode, single address space • Simple • common for sensors/microcontrollers • Protected mode & VM mechanisms can be handled accordingly • Codesize: ~1-2K • TinyOS ~1K • VxWorks ~102K • Linux kernel ~4M • Fault injection with the Bochs simulator

  18. Implementation 1 ) MM_FindFrame: ;(PT, FT, i) ; al contains current frame suggestion ; nf <- (frmae[PT[i]] + 1) modulo M 2 ) and byte [bx+FRAME_COL], FRAME_MASK 3 ) inc al 4 ) and al, FRAME_MASK ;Check all slots for an empty one. ;while nf != frame[PT[i]] and FT[nf] != nil 5 ) while1: 6 ) cmp al, [bx+FRAME_COL] 7 ) jz endwhile1 8 ) lea si, [frames] 9 ) add si, ax 10) mov dl, [si] 11) cmp dl, NULL_PROCESS 12) jz endwhile1 ; do nf <- (nf + 1) modulo M 13) inc al 14) and al, FRAME_MASK 15) jmp while1 16) endwhile1: ; return found frame number in register 'al' 17) ret

  19. Future Work • I/O device drivers • Major cause of operating systems failures • Co-operation of more than one microprocessor • Detailed driver / General monitoring layer • Gather the different parts • Micro-kernel / VMM

  20. Conclusion • The work shows theoretical and practical ways to achieve the goal of a self-stabilizing OS • The (system) research community & industry can benefit from the foundation of self-stabilization • http://www.cs.bgu.ac.il/~yagel/sos

  21. Space Vehicle Failure • …The Spirit rover has a radiation-hardened R6000 CPU from Lockheed-Martin Federal Systems…The operating system is Wind River Systems' Vx-Works.. • …attempted to allocate more files than the RAM-based directory structure could accommodate. That caused an exception, which caused the task that had attempted the allocation to be suspended… • …Spirit fell silent, alone on the emptiness of Mars… http://www.eetimes.com/story/OEG20040220S0046 • …the rover was in fact listening and rebooting, the team commanded Spirit to reboot without mounting the flash file system • …But just in case, the team is working on an exception-handler routine that will more gracefully recover from an allocation failure

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