Messages in this thread | | | From | Yafang Shao <> | Date | Thu, 30 Sep 2021 20:41:40 +0800 | Subject | Re: [PATCH 2/5] kernel/fork: allocate task->comm dynamicly |
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On Thu, Sep 30, 2021 at 2:11 AM Kees Cook <keescook@chromium.org> wrote: > > On Wed, Sep 29, 2021 at 11:50:33AM +0000, Yafang Shao wrote: > > task->comm is defined as an array embedded in struct task_struct before. > > This patch changes it to a char pointer. It will be allocated in the fork > > and freed when the task is freed. > > > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > > --- > > include/linux/sched.h | 2 +- > > kernel/fork.c | 19 +++++++++++++++++++ > > 2 files changed, 20 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index e12b524426b0..b387b5943db4 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1051,7 +1051,7 @@ struct task_struct { > > * - access it with [gs]et_task_comm() > > * - lock it with task_lock() > > */ > > - char comm[TASK_COMM_LEN]; > > + char *comm; > > This, I think, is basically a non-starter. It adds another kmalloc to > the fork path without a well-justified reason. TASK_COMM_LEN is small, > yes, but why is growing it valuable enough to slow things down? > > (Or, can you prove that this does NOT slow things down? It seems like > it would.) >
Right, the new kmalloc would take some extra latency. Seems it is not easy to measure which one is more valuable.
> > > > > struct nameidata *nameidata; > > > > diff --git a/kernel/fork.c b/kernel/fork.c > > index 38681ad44c76..227aec240501 100644 > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -721,6 +721,20 @@ static void mmdrop_async(struct mm_struct *mm) > > } > > } > > > > +static int task_comm_alloc(struct task_struct *p) > > +{ > > + p->comm = kzalloc(TASK_COMM_LEN, GFP_KERNEL); > > + if (!p->comm) > > + return -ENOMEM; > > + > > + return 0; > > +} > > + > > +static void task_comm_free(struct task_struct *p) > > +{ > > + kfree(p->comm); > > +} > > + > > static inline void free_signal_struct(struct signal_struct *sig) > > { > > taskstats_tgid_free(sig); > > @@ -753,6 +767,7 @@ void __put_task_struct(struct task_struct *tsk) > > bpf_task_storage_free(tsk); > > exit_creds(tsk); > > delayacct_tsk_free(tsk); > > + task_comm_free(tsk); > > put_signal_struct(tsk->signal); > > sched_core_free(tsk); > > > > @@ -2076,6 +2091,10 @@ static __latent_entropy struct task_struct *copy_process( > > if (data_race(nr_threads >= max_threads)) > > goto bad_fork_cleanup_count; > > > > + retval = task_comm_alloc(p); > > + if (retval) > > + goto bad_fork_cleanup_count; > > + > > delayacct_tsk_init(p); /* Must remain after dup_task_struct() */ > > p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE | PF_NO_SETAFFINITY); > > p->flags |= PF_FORKNOEXEC; > > -- > > 2.17.1 > > > > -- > Kees Cook
-- Thanks Yafang
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