[PATCH v7 1/3] mm: rearrange madvise code to allow for reuse

Sumit Semwal
2020-09-01T16:15:32Z

From: Colin Cross <ccross@google.com>

Refactor the madvise syscall to allow for parts of it to be reused by a
prctl syscall that affects vmas.

Move the code that walks vmas in a virtual address range into a function
that takes a function pointer as a parameter. The only caller for now is
sys_madvise, which uses it to call madvise_vma_behavior on each vma, but
the next patch will add an additional caller.

Move handling all vma behaviors inside madvise_behavior, and rename it to
madvise_vma_behavior.

Move the code that updates the flags on a vma, including splitting or
merging the vma as necessary, into a new function called
madvise_update_vma. The next patch will add support for updating a new
anon_name field as well.

Signed-off-by: Colin Cross <ccross@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Rob Landley <rob@landley.net>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Shaohua Li <shli@fusionio.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[sumits: rebased over v5.9-rc3]
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
---
mm/madvise.c | 312 +++++++++++++++++++++++++++------------------------
1 file changed, 168 insertions(+), 144 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index dd1d43cf026d..84482c21b029 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -60,76 +60,20 @@ static int madvise_need_mmap_write(int behavior)
}

/*
- * We can potentially split a vm area into separate
- * areas, each area with its own behavior.
+ * Update the vm_flags on regiion of a vma, splitting it or merging it as
+ * necessary. Must be called with mmap_sem held for writing;
*/
-static long madvise_behavior(struct vm_area_struct *vma,
- struct vm_area_struct **prev,
- unsigned long start, unsigned long end, int behavior)
+static int madvise_update_vma(struct vm_area_struct *vma,
+ struct vm_area_struct **prev, unsigned long start,
+ unsigned long end, unsigned long new_flags)
{
struct mm_struct *mm = vma->vm_mm;
- int error = 0;
+ int error;
pgoff_t pgoff;
- unsigned long new_flags = vma->vm_flags;
-
- switch (behavior) {
- case MADV_NORMAL:
- new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
- break;
- case MADV_SEQUENTIAL:
- new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
- break;
- case MADV_RANDOM:
- new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
- break;
- case MADV_DONTFORK:
- new_flags |= VM_DONTCOPY;
- break;
- case MADV_DOFORK:
- if (vma->vm_flags & VM_IO) {
- error = -EINVAL;
- goto out;
- }
- new_flags &= ~VM_DONTCOPY;
- break;
- case MADV_WIPEONFORK:
- /* MADV_WIPEONFORK is only supported on anonymous memory. */
- if (vma->vm_file || vma->vm_flags & VM_SHARED) {
- error = -EINVAL;
- goto out;
- }
- new_flags |= VM_WIPEONFORK;
- break;
- case MADV_KEEPONFORK:
- new_flags &= ~VM_WIPEONFORK;
- break;
- case MADV_DONTDUMP:
- new_flags |= VM_DONTDUMP;
- break;
- case MADV_DODUMP:
- if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) {
- error = -EINVAL;
- goto out;
- }
- new_flags &= ~VM_DONTDUMP;
- break;
- case MADV_MERGEABLE:
- case MADV_UNMERGEABLE:
- error = ksm_madvise(vma, start, end, behavior, &new_flags);
- if (error)
- goto out_convert_errno;
- break;
- case MADV_HUGEPAGE:
- case MADV_NOHUGEPAGE:
- error = hugepage_madvise(vma, &new_flags, behavior);
- if (error)
- goto out_convert_errno;
- break;
- }

if (new_flags == vma->vm_flags) {
*prev = vma;
- goto out;
+ return 0;
}

pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
@@ -146,21 +90,21 @@ static long madvise_behavior(struct vm_area_struct *vma,
if (start != vma->vm_start) {
if (unlikely(mm->map_count >= sysctl_max_map_count)) {
error = -ENOMEM;
- goto out;
+ return error;
}
error = __split_vma(mm, vma, start, 1);
if (error)
- goto out_convert_errno;
+ return error;
}

if (end != vma->vm_end) {
if (unlikely(mm->map_count >= sysctl_max_map_count)) {
error = -ENOMEM;
- goto out;
+ return error;
}
error = __split_vma(mm, vma, end, 0);
if (error)
- goto out_convert_errno;
+ return error;
}

success:
@@ -169,15 +113,7 @@ static long madvise_behavior(struct vm_area_struct *vma,
*/
vma->vm_flags = new_flags;

-out_convert_errno:
- /*
- * madvise() returns EAGAIN if kernel resources, such as
- * slab, are temporarily unavailable.
- */
- if (error == -ENOMEM)
- error = -EAGAIN;
-out:
- return error;
+ return 0;
}

#ifdef CONFIG_SWAP
@@ -862,6 +798,93 @@ static long madvise_remove(struct vm_area_struct *vma,
return error;
}

+/*
+ * Apply an madvise behavior to a region of a vma. madvise_update_vma
+ * will handle splitting a vm area into separate areas, each area with its own
+ * behavior.
+ */
+static int madvise_vma_behavior(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end,
+ unsigned long behavior)
+{
+ int error = 0;
+ unsigned long new_flags = vma->vm_flags;
+
+ switch (behavior) {
+ case MADV_REMOVE:
+ return madvise_remove(vma, prev, start, end);
+ case MADV_WILLNEED:
+ return madvise_willneed(vma, prev, start, end);
+ case MADV_COLD:
+ return madvise_cold(vma, prev, start, end);
+ case MADV_PAGEOUT:
+ return madvise_pageout(vma, prev, start, end);
+ case MADV_FREE:
+ case MADV_DONTNEED:
+ return madvise_dontneed_free(vma, prev, start, end, behavior);
+ case MADV_NORMAL:
+ new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
+ break;
+ case MADV_SEQUENTIAL:
+ new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
+ break;
+ case MADV_RANDOM:
+ new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
+ break;
+ case MADV_DONTFORK:
+ new_flags |= VM_DONTCOPY;
+ break;
+ case MADV_DOFORK:
+ if (vma->vm_flags & VM_IO) {
+ error = -EINVAL;
+ goto out;
+ }
+ new_flags &= ~VM_DONTCOPY;
+ break;
+ case MADV_WIPEONFORK:
+ /* MADV_WIPEONFORK is only supported on anonymous memory. */
+ if (vma->vm_file || vma->vm_flags & VM_SHARED) {
+ error = -EINVAL;
+ goto out;
+ }
+ new_flags |= VM_WIPEONFORK;
+ break;
+ case MADV_KEEPONFORK:
+ new_flags &= ~VM_WIPEONFORK;
+ break;
+ case MADV_DONTDUMP:
+ new_flags |= VM_DONTDUMP;
+ break;
+ case MADV_DODUMP:
+ if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) {
+ error = -EINVAL;
+ goto out;
+ }
+ new_flags &= ~VM_DONTDUMP;
+ break;
+ case MADV_MERGEABLE:
+ case MADV_UNMERGEABLE:
+ error = ksm_madvise(vma, start, end, behavior, &new_flags);
+ if (error)
+ goto out;
+ break;
+ case MADV_HUGEPAGE:
+ case MADV_NOHUGEPAGE:
+ error = hugepage_madvise(vma, &new_flags, behavior);
+ if (error)
+ goto out;
+ break;
+ }
+
+ error = madvise_update_vma(vma, prev, start, end, new_flags);
+
+out:
+ if (error == -ENOMEM)
+ error = -EAGAIN;
+ return error;
+}
+
#ifdef CONFIG_MEMORY_FAILURE
/*
* Error injection support for memory error handling.
@@ -931,27 +954,6 @@ static int madvise_inject_error(int behavior,
}
#endif

-static long
-madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
- unsigned long start, unsigned long end, int behavior)
-{
- switch (behavior) {
- case MADV_REMOVE:
- return madvise_remove(vma, prev, start, end);
- case MADV_WILLNEED:
- return madvise_willneed(vma, prev, start, end);
- case MADV_COLD:
- return madvise_cold(vma, prev, start, end);
- case MADV_PAGEOUT:
- return madvise_pageout(vma, prev, start, end);
- case MADV_FREE:
- case MADV_DONTNEED:
- return madvise_dontneed_free(vma, prev, start, end, behavior);
- default:
- return madvise_behavior(vma, prev, start, end, behavior);
- }
-}
-
static bool
madvise_behavior_valid(int behavior)
{
@@ -990,6 +992,73 @@ madvise_behavior_valid(int behavior)
}
}

+/*
+ * Walk the vmas in range [start,end), and call the visit function on each one.
+ * The visit function will get start and end parameters that cover the overlap
+ * between the current vma and the original range. Any unmapped regions in the
+ * original range will result in this function returning -ENOMEM while still
+ * calling the visit function on all of the existing vmas in the range.
+ * Must be called with the mmap_lock held for reading or writing.
+ */
+static
+int madvise_walk_vmas(unsigned long start, unsigned long end,
+ unsigned long arg,
+ int (*visit)(struct vm_area_struct *vma,
+ struct vm_area_struct **prev, unsigned long start,
+ unsigned long end, unsigned long arg))
+{
+ struct vm_area_struct *vma;
+ struct vm_area_struct *prev;
+ unsigned long tmp;
+ int unmapped_error = 0;
+
+ /*
+ * If the interval [start,end) covers some unmapped address
+ * ranges, just ignore them, but return -ENOMEM at the end.
+ * - different from the way of handling in mlock etc.
+ */
+ vma = find_vma_prev(current->mm, start, &prev);
+ if (vma && start > vma->vm_start)
+ prev = vma;
+
+ for (;;) {
+ int error;
+
+ /* Still start < end. */
+ if (!vma)
+ return -ENOMEM;
+
+ /* Here start < (end|vma->vm_end). */
+ if (start < vma->vm_start) {
+ unmapped_error = -ENOMEM;
+ start = vma->vm_start;
+ if (start >= end)
+ break;
+ }
+
+ /* Here vma->vm_start <= start < (end|vma->vm_end) */
+ tmp = vma->vm_end;
+ if (end < tmp)
+ tmp = end;
+
+ /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
+ error = visit(vma, &prev, start, tmp, arg);
+ if (error)
+ return error;
+ start = tmp;
+ if (prev && start < prev->vm_end)
+ start = prev->vm_end;
+ if (start >= end)
+ break;
+ if (prev)
+ vma = prev->vm_next;
+ else /* madvise_remove dropped mmap_lock */
+ vma = find_vma(current->mm, start);
+ }
+
+ return unmapped_error;
+}
+
/*
* The madvise(2) system call.
*
@@ -1053,9 +1122,7 @@ madvise_behavior_valid(int behavior)
*/
int do_madvise(unsigned long start, size_t len_in, int behavior)
{
- unsigned long end, tmp;
- struct vm_area_struct *vma, *prev;
- int unmapped_error = 0;
+ unsigned long end;
int error = -EINVAL;
int write;
size_t len;
@@ -1112,51 +1179,8 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
mmap_read_lock(current->mm);
}

- /*
- * If the interval [start,end) covers some unmapped address
- * ranges, just ignore them, but return -ENOMEM at the end.
- * - different from the way of handling in mlock etc.
- */
- vma = find_vma_prev(current->mm, start, &prev);
- if (vma && start > vma->vm_start)
- prev = vma;
-
blk_start_plug(&plug);
- for (;;) {
- /* Still start < end. */
- error = -ENOMEM;
- if (!vma)
- goto out;
-
- /* Here start < (end|vma->vm_end). */
- if (start < vma->vm_start) {
- unmapped_error = -ENOMEM;
- start = vma->vm_start;
- if (start >= end)
- goto out;
- }
-
- /* Here vma->vm_start <= start < (end|vma->vm_end) */
- tmp = vma->vm_end;
- if (end < tmp)
- tmp = end;
-
- /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
- error = madvise_vma(vma, &prev, start, tmp, behavior);
- if (error)
- goto out;
- start = tmp;
- if (prev && start < prev->vm_end)
- start = prev->vm_end;
- error = unmapped_error;
- if (start >= end)
- goto out;
- if (prev)
- vma = prev->vm_next;
- else /* madvise_remove dropped mmap_lock */
- vma = find_vma(current->mm, start);
- }
-out:
+ error = madvise_walk_vmas(start, end, behavior, madvise_vma_behavior);
blk_finish_plug(&plug);
if (write)
mmap_write_unlock(current->mm);
--
2.28.0