On 8/5/25 1:15 AM, Suren Baghdasaryan wrote:
Utilize per-vma locks to stabilize vma after lookup without taking mmap_lock during PROCMAP_QUERY ioctl execution. If vma lock is contended, we fall back to mmap_lock but take it only momentarily to lock the vma and release the mmap_lock. In a very unlikely case of vm_refcnt overflow, this fall back path will fail and ioctl is done under mmap_lock protection.
This change is designed to reduce mmap_lock contention and prevent PROCMAP_QUERY ioctl calls from blocking address space updates.
Signed-off-by: Suren Baghdasaryan surenb@google.com
fs/proc/task_mmu.c | 81 +++++++++++++++++++++++++++++++++++++--------- 1 file changed, 65 insertions(+), 16 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 843577aa7a32..1d06ecdbef6f 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -517,28 +517,78 @@ static int pid_maps_open(struct inode *inode, struct file *file) PROCMAP_QUERY_VMA_FLAGS \ ) -static int query_vma_setup(struct mm_struct *mm) +#ifdef CONFIG_PER_VMA_LOCK
+static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx) {
- return mmap_read_lock_killable(mm);
- lock_ctx->locked_vma = NULL;
- lock_ctx->mmap_locked = false;
- return 0;
} -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma) +static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx) {
- mmap_read_unlock(mm);
- if (lock_ctx->mmap_locked)
mmap_read_unlock(lock_ctx->mm);- else
unlock_vma(lock_ctx);} -static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr) +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx,
unsigned long addr){
- return find_vma(mm, addr);
- struct vm_area_struct *vma;
- struct vma_iterator vmi;
Hm I think we can reach here with lock_ctx->mmap_locked being true via "goto next_vma" in query_matching_vma(). In that case we should just "return find_vma()" and doing the below is wrong, no?
- unlock_vma(lock_ctx);
- rcu_read_lock();
- vma_iter_init(&vmi, lock_ctx->mm, addr);
- vma = lock_next_vma(lock_ctx->mm, &vmi, addr);
- rcu_read_unlock();
- if (!IS_ERR_OR_NULL(vma)) {
lock_ctx->locked_vma = vma;- } else if (PTR_ERR(vma) == -EAGAIN) {
/* Fallback to mmap_lock on vma->vm_refcnt overflow */mmap_read_lock(lock_ctx->mm);vma = find_vma(lock_ctx->mm, addr);lock_ctx->mmap_locked = true;- }
- return vma;
}