kgdb: fix SMP NMI kgdb_handle_exception exit race (56fb7093) · Commits · 戴 / test

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>

kernel/kgdb.c

+8 −19

Original line number	Diff line number	Diff line
		@@ -561,18 +561,6 @@ static void kgdb_wait(struct pt_regs *regs)
		smp_wmb();
		atomic_set(&cpu_in_kgdb[cpu], 1);

		/*
		* The primary CPU must be active to enter here, but this is
		* guard in case the primary CPU had not been selected if
		* this was an entry via nmi.
		*/
		while (atomic_read(&kgdb_active) == -1)
		cpu_relax();

		/* Wait till primary CPU goes completely into the debugger. */
		while (!atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)]))
		cpu_relax();

		/* Wait till primary CPU is done with debugging */
		while (atomic_read(&passive_cpu_wait[cpu]))
		cpu_relax();
		@@ -1447,18 +1435,18 @@ acquirelock:
		atomic_set(&passive_cpu_wait[i], 1);
		}

		#ifdef CONFIG_SMP
		/* Signal the other CPUs to enter kgdb_wait() */
		if ((!kgdb_single_step \|\| !kgdb_contthread) && kgdb_do_roundup)
		kgdb_roundup_cpus(flags);
		#endif

		/*
		* spin_lock code is good enough as a barrier so we don't
		* need one here:
		*/
		atomic_set(&cpu_in_kgdb[ks->cpu], 1);

		#ifdef CONFIG_SMP
		/* Signal the other CPUs to enter kgdb_wait() */
		if ((!kgdb_single_step \|\| !kgdb_contthread) && kgdb_do_roundup)
		kgdb_roundup_cpus(flags);
		#endif

		/*
		* Wait for the other CPUs to be notified and be waiting for us:
		*/
		@@ -1514,7 +1502,8 @@ int kgdb_nmicallback(int cpu, void *regs)
		{
		#ifdef CONFIG_SMP
		if (!atomic_read(&cpu_in_kgdb[cpu]) &&
		atomic_read(&kgdb_active) != cpu) {
		atomic_read(&kgdb_active) != cpu &&
		atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
		kgdb_wait((struct pt_regs *)regs);
		return 0;
		}

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