Commit 4d45e75a authored by Jann Horn's avatar Jann Horn Committed by Linus Torvalds
Browse files

mm: remove the now-unnecessary mmget_still_valid() hack 



The preceding patches have ensured that core dumping properly takes the
mmap_lock.  Thanks to that, we can now remove mmget_still_valid() and all
its users.

Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200827114932.3572699-8-jannh@google.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7f3bfab5

drivers/infiniband/core/uverbs_main.c

+0 −3
Original line number Diff line number Diff line
@@ -845,8 +845,6 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile) 
		 * will only be one mm, so no big deal.

		 */

		mmap_read_lock(mm);

		if (!mmget_still_valid(mm))

			goto skip_mm;

		mutex_lock(&ufile->umap_lock);

		list_for_each_entry_safe (priv, next_priv, &ufile->umaps,

					  list) {
@@ -865,7 +863,6 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile) 
			}

		}

		mutex_unlock(&ufile->umap_lock);

	skip_mm:

		mmap_read_unlock(mm);

		mmput(mm);

	}

drivers/vfio/pci/vfio_pci.c

+18 −20
Original line number Diff line number Diff line
@@ -1480,7 +1480,6 @@ static int vfio_pci_zap_and_vma_lock(struct vfio_pci_device *vdev, bool try) 
		} else {

			mmap_read_lock(mm);

		}

		if (mmget_still_valid(mm)) {

		if (try) {

			if (!mutex_trylock(&vdev->vma_lock)) {

				mmap_read_unlock(mm);
@@ -1504,7 +1503,6 @@ static int vfio_pci_zap_and_vma_lock(struct vfio_pci_device *vdev, bool try) 
				     vma->vm_end - vma->vm_start);

		}

		mutex_unlock(&vdev->vma_lock);

		}

		mmap_read_unlock(mm);

		mmput(mm);

	}

fs/proc/task_mmu.c

+0 −18
Original line number Diff line number Diff line
@@ -1244,24 +1244,6 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, 
					count = -EINTR;

					goto out_mm;

				}

				/*

				 * Avoid to modify vma->vm_flags

				 * without locked ops while the

				 * coredump reads the vm_flags.

				 */

				if (!mmget_still_valid(mm)) {

					/*

					 * Silently return "count"

					 * like if get_task_mm()

					 * failed. FIXME: should this

					 * function have returned

					 * -ESRCH if get_task_mm()

					 * failed like if

					 * get_proc_task() fails?

					 */

					mmap_write_unlock(mm);

					goto out_mm;

				}

				for (vma = mm->mmap; vma; vma = vma->vm_next) {

					vma->vm_flags &= ~VM_SOFTDIRTY;

					vma_set_page_prot(vma);

fs/userfaultfd.c

+9 −19
Original line number Diff line number Diff line
@@ -601,8 +601,6 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, 


		/* the various vma->vm_userfaultfd_ctx still points to it */

		mmap_write_lock(mm);

		/* no task can run (and in turn coredump) yet */

		VM_WARN_ON(!mmget_still_valid(mm));

		for (vma = mm->mmap; vma; vma = vma->vm_next)

			if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {

				vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
@@ -842,7 +840,6 @@ static int userfaultfd_release(struct inode *inode, struct file *file) 
	/* len == 0 means wake all */

	struct userfaultfd_wake_range range = { .len = 0, };

	unsigned long new_flags;

	bool still_valid;



	WRITE_ONCE(ctx->released, true);
@@ -858,7 +855,6 @@ static int userfaultfd_release(struct inode *inode, struct file *file) 
	 * taking the mmap_lock for writing.

	 */

	mmap_write_lock(mm);

	still_valid = mmget_still_valid(mm);

	prev = NULL;

	for (vma = mm->mmap; vma; vma = vma->vm_next) {

		cond_resched();
@@ -869,7 +865,6 @@ static int userfaultfd_release(struct inode *inode, struct file *file) 
			continue;

		}

		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);

		if (still_valid) {

		prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,

				 new_flags, vma->anon_vma,

				 vma->vm_file, vma->vm_pgoff,
@@ -879,7 +874,6 @@ static int userfaultfd_release(struct inode *inode, struct file *file) 
			vma = prev;

		else

			prev = vma;

		}

		vma->vm_flags = new_flags;

		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;

	}
@@ -1309,8 +1303,6 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, 
		goto out;



	mmap_write_lock(mm);

	if (!mmget_still_valid(mm))

		goto out_unlock;

	vma = find_vma_prev(mm, start, &prev);

	if (!vma)

		goto out_unlock;
@@ -1511,8 +1503,6 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, 
		goto out;



	mmap_write_lock(mm);

	if (!mmget_still_valid(mm))

		goto out_unlock;

	vma = find_vma_prev(mm, start, &prev);

	if (!vma)

		goto out_unlock;

include/linux/sched/mm.h

+0 −25
Original line number Diff line number Diff line
@@ -49,31 +49,6 @@ static inline void mmdrop(struct mm_struct *mm) 
		__mmdrop(mm);

}



/*

 * This has to be called after a get_task_mm()/mmget_not_zero()

 * followed by taking the mmap_lock for writing before modifying the

 * vmas or anything the coredump pretends not to change from under it.

 *

 * It also has to be called when mmgrab() is used in the context of

 * the process, but then the mm_count refcount is transferred outside

 * the context of the process to run down_write() on that pinned mm.

 *

 * NOTE: find_extend_vma() called from GUP context is the only place

 * that can modify the "mm" (notably the vm_start/end) under mmap_lock

 * for reading and outside the context of the process, so it is also

 * the only case that holds the mmap_lock for reading that must call

 * this function. Generally if the mmap_lock is hold for reading

 * there's no need of this check after get_task_mm()/mmget_not_zero().

 *

 * This function can be obsoleted and the check can be removed, after

 * the coredump code will hold the mmap_lock for writing before

 * invoking the ->core_dump methods.

 */

static inline bool mmget_still_valid(struct mm_struct *mm)

{

	return likely(!mm->core_state);

}



/**

 * mmget() - Pin the address space associated with a &struct mm_struct.

 * @mm: The address space to pin.