Messages in this thread | | | Date | Thu, 23 Aug 2012 18:43:15 +0400 | From | Glauber Costa <> | Subject | Re: [PATCH] fork: fix oops after fork failure |
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On 08/23/2012 06:45 PM, Michal Hocko wrote: > On Thu 23-08-12 16:38:50, Michal Hocko wrote: >> On Thu 23-08-12 16:33:12, Michal Hocko wrote: >>> On Thu 23-08-12 17:08:46, Glauber Costa wrote: >>>> When we want to duplicate a new process, dup_task_struct() will undergo >>>> a series of allocations. If alloc_thread_info_node() fails, we call >>>> free_task_struct() and return. >>>> >>>> This seems right, but it is not. free_task_struct() will not only free >>>> the task struct from the kmem_cache, but will also call >>>> arch_release_task_struct(). The problem is that this function is >>>> supposed to undo whatever arch-specific work done by >>>> arch_dup_task_struct(), that is not yet called at this point. The >>>> particular problem I ran accross was that in x86, we will arrive at >>>> fpu_free() without having ever allocated it. >>>> >>>> This code is very ancient, and according to git, it is there since the >>>> pre-git era. But forks don't fail that often, so that made it well >>>> hidden. >>>> >>>> Signed-off-by: Glauber Costa <glommer@parallels.com> >>>> Reported-by: Frederic Weisbecker <fweisbec@redhat.com> >>>> --- >>>> kernel/fork.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/kernel/fork.c b/kernel/fork.c >>>> index 152d023..b397435 100644 >>>> --- a/kernel/fork.c >>>> +++ b/kernel/fork.c >>>> @@ -299,7 +299,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) >>>> >>>> ti = alloc_thread_info_node(tsk, node); >>>> if (!ti) { >>>> - free_task_struct(tsk); >>>> + kmem_cache_free(task_struct_cachep, tsk); >>> >>> What about ia64 (or !CONFIG_ARCH_THREAD_INFO_ALLOCATOR in general) which >>> doesn't allocate thread_info at all? >> >> Hit send button too fast. Should read (or CONFIG_ARCH_THREAD_INFO_ALLOCATOR) >> ia64 will not fail obviously and there is no other arch which would >> define own thread infor allocators but there might be some in future. > > Bahh, and I should have been looking at CONFIG_ARCH_TASK_STRUCT_ALLOCATOR > instead. Anyway ia64 uses page allocator directly so kmem_cache_free is > not appropriate. > Yes, you are right. Thanks for spotting this
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