Messages in this thread | | | Date | Fri, 27 Oct 2023 12:11:47 +0530 | Subject | Re: [PATCH v3] Fixing directly deferencing a __rcu pointer warning | From | Abhinav Singh <> |
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On 10/27/23 12:07, Abhinav Singh wrote: > This patch fixes the warning about directly dereferencing a pointer > tagged with __rcu annotation. > > Dereferencing the pointers tagged with __rcu directly should > always be avoided according to the docs. There is a rcu helper > functions rcu_dereference(...) to use when dereferencing a __rcu > pointer. This functions returns the non __rcu tagged pointer which > can be dereferenced just like a normal pointers. > > > Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com> > --- > kernel/fork.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 10917c3e1f03..e78649974669 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -2369,7 +2369,7 @@ __latent_entropy struct task_struct *copy_process( > > retval = -EAGAIN; > if (is_rlimit_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) { > - if (p->real_cred->user != INIT_USER && > + if (rcu_dereference(p->real_cred)->user != INIT_USER && > !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) > goto bad_fork_cleanup_count; > } > @@ -2690,9 +2690,9 @@ __latent_entropy struct task_struct *copy_process( > * tasklist_lock with adding child to the process tree > * for propagate_has_child_subreaper optimization. > */ > - p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper || > - p->real_parent->signal->is_child_subreaper; > - list_add_tail(&p->sibling, &p->real_parent->children); > + p->signal->has_child_subreaper = rcu_dereference(p->real_parent)->signal->has_child_subreaper || > + rcu_dereference(p->real_parent)->signal->is_child_subreaper; > + list_add_tail(&p->sibling, &rcu_dereference(p->real_parent)->children); > list_add_tail_rcu(&p->tasks, &init_task.tasks); > attach_pid(p, PIDTYPE_TGID); > attach_pid(p, PIDTYPE_PGID);
For this particular file I have resolved the rcu pointer dereferencing issue and I have tested the above by using qemu using this command qemu-system-x86_64 \ -m 2G \ -smp 2 \ -kernel /home/abhinav/linux_work/linux/arch/x86/boot/bzImage \ -append "console=ttyS0 root=/dev/sda earlyprintk=serial net.ifnames=0" \ -drive file=/home/abhinav/linux_work/boot_images/bullseye.img,format=raw \ -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \ -net nic,model=e1000 \ -enable-kvm \ -nographic \ -pidfile vm.pid \ 2>&1 | tee vm.log it booted without any issues.
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