forked from luck/tmp_suning_uos_patched
kgdb: fix SMP NMI kgdb_handle_exception exit race
Fix the problem of protecting the kgdb handle_exception exit which had an NMI race condition, while trying to restore normal system operation. There was a small window after the master processor sets cpu_in_debug to zero but before it has set kgdb_active to zero where a non-master processor in an SMP system could receive an NMI and re-enter the kgdb_wait() loop. As long as the master processor sets the cpu_in_debug before sending the cpu roundup the cpu_in_debug variable can also be used to guard against the race condition. The kgdb_wait() function no longer needs to check kgdb_active because it is done in the arch specific code and handled along with the nmi traps at the low level. This also allows kgdb_wait() to exit correctly if it was entered for some unknown reason due to a spurious NMI that could not be handled by the arch specific code. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -561,18 +561,6 @@ static void kgdb_wait(struct pt_regs *regs)
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smp_wmb();
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atomic_set(&cpu_in_kgdb[cpu], 1);
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/*
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* The primary CPU must be active to enter here, but this is
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* guard in case the primary CPU had not been selected if
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* this was an entry via nmi.
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*/
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while (atomic_read(&kgdb_active) == -1)
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cpu_relax();
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/* Wait till primary CPU goes completely into the debugger. */
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while (!atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)]))
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cpu_relax();
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/* Wait till primary CPU is done with debugging */
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while (atomic_read(&passive_cpu_wait[cpu]))
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cpu_relax();
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@ -1447,18 +1435,18 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
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atomic_set(&passive_cpu_wait[i], 1);
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}
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#ifdef CONFIG_SMP
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/* Signal the other CPUs to enter kgdb_wait() */
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if ((!kgdb_single_step || !kgdb_contthread) && kgdb_do_roundup)
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kgdb_roundup_cpus(flags);
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#endif
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/*
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* spin_lock code is good enough as a barrier so we don't
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* need one here:
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*/
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atomic_set(&cpu_in_kgdb[ks->cpu], 1);
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#ifdef CONFIG_SMP
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/* Signal the other CPUs to enter kgdb_wait() */
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if ((!kgdb_single_step || !kgdb_contthread) && kgdb_do_roundup)
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kgdb_roundup_cpus(flags);
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#endif
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/*
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* Wait for the other CPUs to be notified and be waiting for us:
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*/
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@ -1514,7 +1502,8 @@ int kgdb_nmicallback(int cpu, void *regs)
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{
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#ifdef CONFIG_SMP
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if (!atomic_read(&cpu_in_kgdb[cpu]) &&
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atomic_read(&kgdb_active) != cpu) {
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atomic_read(&kgdb_active) != cpu &&
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atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
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kgdb_wait((struct pt_regs *)regs);
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return 0;
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}
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