Am 28.02.22 um 12:08 schrieb Jakob Koschel:
If the list does not contain the expected element, the value of
list_for_each_entry() iterator will not point to a valid structure.
To avoid type confusion in such case, the list iterator
scope will be limited to list_for_each_entry() loop.
We explicitly have the list_entry_is_head() macro to test after a loop
if the element pointer points to the head of the list instead of a valid
list entry.
So at least from my side I absolutely don't think that this is a good idea.
In preparation to limiting scope of a list iterator to the list traversal
loop, use a dedicated pointer to point to the found element.
Determining if an element was found is then simply checking if
the pointer is != NULL.
Since when do we actually want to do this?
Take this code here as an example:
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 48afe96ae0f0..6c916416decc 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -450,7 +450,8 @@ static void sgx_mmu_notifier_release(struct mmu_notifier
*mn,
struct mm_struct *mm)
{
struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm,
mmu_notifier);
- struct sgx_encl_mm *tmp = NULL;
+ struct sgx_encl_mm *found_encl_mm = NULL;
+ struct sgx_encl_mm *tmp;
/*
* The enclave itself can remove encl_mm. Note, objects can't be moved
@@ -460,12 +461,13 @@ static void sgx_mmu_notifier_release(struct mmu_notifier
*mn,
list_for_each_entry(tmp, &encl_mm->encl->mm_list, list) {
if (tmp == encl_mm) {
list_del_rcu(&encl_mm->list);
+ found_encl_mm = tmp;
break;
}
}
spin_unlock(&encl_mm->encl->mm_lock);
- if (tmp == encl_mm) {
+ if (found_encl_mm) {
synchronize_srcu(&encl_mm->encl->srcu);
mmu_notifier_put(mn);
}
I don't think that using the extra variable makes the code in any way
more reliable or easier to read.
Regards,
Christian.
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