Messages in this thread Patch in this message | | | From | Abhinav Singh <> | Subject | [PATCH v3] Fixing directly deferencing a __rcu pointer warning | Date | Sun, 29 Oct 2023 02:16:09 +0530 |
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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 function rcu_dereference(...) to use when dereferencing a __rcu pointer inside rcu read side critical sections. This function returns the non __rcu tagged pointer which can be dereferenced just like a normal pointer.
Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com> ---
Link to original patch https://lore.kernel.org/all/20231025222811.855336-1-singhabhinav9051571833@gmail.com/
Change from original -> v2 : 1. removed the null check before dereferencing the dereferenced rcu pointer at line 2372. 2. added rcu_dereference(...) at line 2694 Changes from v2 -> v3 1. added rcu_dereference(...) at line 2693
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); -- 2.39.2
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