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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: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Linus 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: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jann Horn 2020-10-15 20:13:00 -07:00 committed by Linus Torvalds
parent 7f3bfab52c
commit 4d45e75a99
8 changed files with 32 additions and 110 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/infiniband/core/uverbs_main.c
View File

@ -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);
}

44
drivers/vfio/pci/vfio_pci.c
View File

@ -1480,31 +1480,29 @@ 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);
mmput(mm);
return 0;
}
} else {
mutex_lock(&vdev->vma_lock);
if (try) {
if (!mutex_trylock(&vdev->vma_lock)) {
mmap_read_unlock(mm);
mmput(mm);
return 0;
}
list_for_each_entry_safe(mmap_vma, tmp,
&vdev->vma_list, vma_next) {
struct vm_area_struct *vma = mmap_vma->vma;
if (vma->vm_mm != mm)
continue;
list_del(&mmap_vma->vma_next);
kfree(mmap_vma);
zap_vma_ptes(vma, vma->vm_start,
vma->vm_end - vma->vm_start);
}
mutex_unlock(&vdev->vma_lock);
} else {
mutex_lock(&vdev->vma_lock);
}
list_for_each_entry_safe(mmap_vma, tmp,
&vdev->vma_list, vma_next) {
struct vm_area_struct *vma = mmap_vma->vma;
if (vma->vm_mm != mm)
continue;
list_del(&mmap_vma->vma_next);
kfree(mmap_vma);
zap_vma_ptes(vma, vma->vm_start,
vma->vm_end - vma->vm_start);
}
mutex_unlock(&vdev->vma_lock);
mmap_read_unlock(mm);
mmput(mm);
}

18
fs/proc/task_mmu.c
View File

@ -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);

28
fs/userfaultfd.c
View File

@ -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();
@ -869,17 +865,15 @@ 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,
vma_policy(vma),
NULL_VM_UFFD_CTX);
if (prev)
vma = prev;
else
prev = vma;
}
prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
new_flags, vma->anon_vma,
vma->vm_file, vma->vm_pgoff,
vma_policy(vma),
NULL_VM_UFFD_CTX);
if (prev)
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;

25
include/linux/sched/mm.h
View File

@ -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.

2
mm/khugepaged.c
View File

@ -434,7 +434,7 @@ static void insert_to_mm_slots_hash(struct mm_struct *mm,
static inline int khugepaged_test_exit(struct mm_struct *mm)
{
return atomic_read(&mm->mm_users) == 0 || !mmget_still_valid(mm);
return atomic_read(&mm->mm_users) == 0;
}
static bool hugepage_vma_check(struct vm_area_struct *vma,

17
mm/madvise.c
View File

@ -1085,23 +1085,6 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
if (write) {
if (mmap_write_lock_killable(current->mm))
return -EINTR;
/*
* We may have stolen the mm from another process
* that is undergoing core dumping.
*
* Right now that's io_ring, in the future it may
* be remote process management and not "current"
* at all.
*
* We need to fix core dumping to not do this,
* but for now we have the mmget_still_valid()
* model.
*/
if (!mmget_still_valid(current->mm)) {
mmap_write_unlock(current->mm);
return -EINTR;
}
} else {
mmap_read_lock(current->mm);
}

5
mm/mmap.c
View File

@ -2562,7 +2562,7 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
if (vma && (vma->vm_start <= addr))
return vma;
/* don't alter vm_end if the coredump is running */
if (!prev || !mmget_still_valid(mm) || expand_stack(prev, addr))
if (!prev || expand_stack(prev, addr))
return NULL;
if (prev->vm_flags & VM_LOCKED)
populate_vma_page_range(prev, addr, prev->vm_end, NULL);
@ -2588,9 +2588,6 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
return vma;
if (!(vma->vm_flags & VM_GROWSDOWN))
return NULL;
/* don't alter vm_start if the coredump is running */
if (!mmget_still_valid(mm))
return NULL;
start = vma->vm_start;
if (expand_stack(vma, addr))
return NULL;