Re: [PATCH] kvm-all: Use 'tmpcpu' instead of 'cpu' in sub-looping to avoid 'cpu' be NULL

Chen Gang
2014-07-20T08:29:18Z

On 07/20/2014 03:29 PM, Jan Kiszka wrote:
> On 2014-07-19 03:21, Chen Gang wrote:
>> If kvm_arch_remove_sw_breakpoint() in CPU_FOREACH() always be fail, it
>> will let 'cpu' NULL. And the next kvm_arch_remove_sw_breakpoint() in
>> QTAILQ_FOREACH_SAFE() will get NULL parameter for 'cpu'.
>>
>> And kvm_arch_remove_sw_breakpoint() can assumes 'cpu' must never be NULL,
>> so need define additional temporary variable for 'cpu' to avoid the case.
>>
>>
>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
>> ---
>> kvm-all.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/kvm-all.c b/kvm-all.c
>> index 3ae30ee..1402f4f 100644
>> --- a/kvm-all.c
>> +++ b/kvm-all.c
>> @@ -2077,12 +2077,13 @@ void kvm_remove_all_breakpoints(CPUState *cpu)
>> {
>> struct kvm_sw_breakpoint *bp, *next;
>> KVMState *s = cpu->kvm_state;
>> + CPUState *tmpcpu;
>>
>> QTAILQ_FOREACH_SAFE(bp, &s->kvm_sw_breakpoints, entry, next) {
>> if (kvm_arch_remove_sw_breakpoint(cpu, bp) != 0) {
>> /* Try harder to find a CPU that currently sees the breakpoint. */
>> - CPU_FOREACH(cpu) {
>> - if (kvm_arch_remove_sw_breakpoint(cpu, bp) == 0) {
>> + CPU_FOREACH(tmpcpu) {
>> + if (kvm_arch_remove_sw_breakpoint(tmpcpu, bp) == 0) {
>> break;
>> }
>> }
>>
>
> Good catch. To make it clear in the changelog: The actual issue is that
> we misuse "cpu" as an iteration variable while its original value is
> still in use. That cpu can eventually become NULL this way is one result.
>

OK, thanks. If necessary, I shall send patch v2 for additional comments.
(if really necessary to send, please let me know)

Thanks.
--
Chen Gang

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