[PATCH] mm: anonymous shared memory naming

Pasha Tatashin
2022-11-05T02:53:51Z

Since:
commit 9a10064f5625 ("mm: add a field to store names for private anonymous
memory")

We can set names for private anonymous memory but not for shared
anonymous memory. However, naming shared anonymous memory just as
useful for tracking purposes.

Extend the functionality to be able to set names for shared anon.

/ [anon_shmem:<name>] an anonymous shared memory mapping that has
been named by userspace

Sample output:
share = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, -1, 0);
rv = prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
share, SIZE, "shared anon");

/proc/<pid>/maps (and smaps):
7fc8e2b4c000-7fc8f2b4c000 rw-s 00000000 00:01 1024
/dev/zero (deleted) [anon_shmem:shared anon]

pmap $(pgrep a.out)
254: pub/a.out
000056093fab2000 4K r---- a.out
000056093fab3000 4K r-x-- a.out
000056093fab4000 4K r---- a.out
000056093fab5000 4K r---- a.out
000056093fab6000 4K rw--- a.out
000056093fdeb000 132K rw--- [ anon ]
00007fc8e2b4c000 262144K rw-s- zero (deleted) [anon_shmem:shared anon]

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
Documentation/filesystems/proc.rst | 4 +++-
fs/proc/task_mmu.c | 7 ++++---
include/linux/mm.h | 2 ++
include/linux/mm_types.h | 27 +++++++++++++--------------
mm/madvise.c | 7 ++-----
mm/shmem.c | 13 +++++++++++--
6 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 898c99eae8e4..8f1e68460da5 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -431,8 +431,10 @@ is not associated with a file:
[stack] the stack of the main process
[vdso] the "virtual dynamic shared object",
the kernel system call handler
- [anon:<name>] an anonymous mapping that has been
+ [anon:<name>] a private anonymous mapping that has been
named by userspace
+ path [anon_shmem:<name>] an anonymous shared memory mapping that has
+ been named by userspace
============= ====================================

or if empty, the mapping is anonymous.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 8a74cdcc9af0..d6ae75ed81ca 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -277,6 +277,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
struct mm_struct *mm = vma->vm_mm;
struct file *file = vma->vm_file;
vm_flags_t flags = vma->vm_flags;
+ struct anon_vma_name *anon_name;
unsigned long ino = 0;
unsigned long long pgoff = 0;
unsigned long start, end;
@@ -293,6 +294,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
start = vma->vm_start;
end = vma->vm_end;
show_vma_header_prefix(m, start, end, flags, pgoff, dev, ino);
+ anon_name = anon_vma_name(vma);

/*
* Print the dentry name for named mappings, and a
@@ -301,6 +303,8 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
if (file) {
seq_pad(m, ' ');
seq_file_path(m, file, "\n");
+ if (anon_name)
+ seq_printf(m, " [anon_shmem:%s]", anon_name->name);
goto done;
}

@@ -312,8 +316,6 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)

name = arch_vma_name(vma);
if (!name) {
- struct anon_vma_name *anon_name;
-
if (!mm) {
name = "[vdso]";
goto done;
@@ -330,7 +332,6 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
goto done;
}

- anon_name = anon_vma_name(vma);
if (anon_name) {
seq_pad(m, ' ');
seq_printf(m, "[anon:%s]", anon_name->name);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8bbcccbc5565..06b6fb3277ab 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -699,8 +699,10 @@ static inline unsigned long vma_iter_addr(struct vma_iterator *vmi)
* paths in userfault.
*/
bool vma_is_shmem(struct vm_area_struct *vma);
+bool vma_is_anon_shmem(struct vm_area_struct *vma);
#else
static inline bool vma_is_shmem(struct vm_area_struct *vma) { return false; }
+static inline bool vma_is_anon_shmem(struct vm_area_struct *vma) { return false; }
#endif

int vma_is_stack_for_current(struct vm_area_struct *vma);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 500e536796ca..08d8b973fb60 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -461,21 +461,11 @@ struct vm_area_struct {
* For areas with an address space and backing store,
* linkage into the address_space->i_mmap interval tree.
*
- * For private anonymous mappings, a pointer to a null terminated string
- * containing the name given to the vma, or NULL if unnamed.
*/
-
- union {
- struct {
- struct rb_node rb;
- unsigned long rb_subtree_last;
- } shared;
- /*
- * Serialized by mmap_sem. Never use directly because it is
- * valid only when vm_file is NULL. Use anon_vma_name instead.
- */
- struct anon_vma_name *anon_name;
- };
+ struct {
+ struct rb_node rb;
+ unsigned long rb_subtree_last;
+ } shared;

/*
* A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
@@ -485,6 +475,7 @@ struct vm_area_struct {
*/
struct list_head anon_vma_chain; /* Serialized by mmap_lock &
* page_table_lock */
+
struct anon_vma *anon_vma; /* Serialized by page_table_lock */

/* Function pointers to deal with this struct. */
@@ -496,6 +487,14 @@ struct vm_area_struct {
struct file * vm_file; /* File we map to (can be NULL). */
void * vm_private_data; /* was vm_pte (shared mem) */

+#ifdef CONFIG_ANON_VMA_NAME
+ /*
+ * For private and shared anonymous mappings, a pointer to a null
+ * terminated string containing the name given to the vma, or NULL if
+ * unnamed. Serialized by mmap_sem. Use anon_vma_name to access.
+ */
+ struct anon_vma_name *anon_name;
+#endif
#ifdef CONFIG_SWAP
atomic_long_t swap_readahead_info;
#endif
diff --git a/mm/madvise.c b/mm/madvise.c
index c7105ec6d08c..255d5b485432 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -95,9 +95,6 @@ struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
{
mmap_assert_locked(vma->vm_mm);

- if (vma->vm_file)
- return NULL;
-
return vma->anon_name;
}

@@ -183,7 +180,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
* vm_flags is protected by the mmap_lock held in write mode.
*/
vma->vm_flags = new_flags;
- if (!vma->vm_file) {
+ if (!vma->vm_file || vma_is_anon_shmem(vma)) {
error = replace_anon_vma_name(vma, anon_name);
if (error)
return error;
@@ -1273,7 +1270,7 @@ static int madvise_vma_anon_name(struct vm_area_struct *vma,
int error;

/* Only anonymous mappings can be named */
- if (vma->vm_file)
+ if (vma->vm_file && !vma_is_anon_shmem(vma))
return -EBADF;

error = madvise_update_vma(vma, prev, start, end, vma->vm_flags,
diff --git a/mm/shmem.c b/mm/shmem.c
index c1d8b8a1aa3b..638bcb3d26bd 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -237,11 +237,17 @@ static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
static const struct vm_operations_struct shmem_vm_ops;
+static const struct vm_operations_struct shmem_anon_vm_ops;
static struct file_system_type shmem_fs_type;

+bool vma_is_anon_shmem(struct vm_area_struct *vma)
+{
+ return vma->vm_ops == &shmem_anon_vm_ops;
+}
+
bool vma_is_shmem(struct vm_area_struct *vma)
{
- return vma->vm_ops == &shmem_vm_ops;
+ return vma_is_anon_shmem(vma) || vma->vm_ops == &shmem_vm_ops;
}

static LIST_HEAD(shmem_swaplist);
@@ -3995,6 +4001,8 @@ static const struct vm_operations_struct shmem_vm_ops = {
#endif
};

+static const struct vm_operations_struct shmem_anon_vm_ops = shmem_vm_ops;
+
int shmem_init_fs_context(struct fs_context *fc)
{
struct shmem_options *ctx;
@@ -4170,6 +4178,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
EXPORT_SYMBOL_GPL(shmem_truncate_range);

#define shmem_vm_ops generic_file_vm_ops
+#define shmem_anon_vm_ops generic_file_vm_ops
#define shmem_file_operations ramfs_file_operations
#define shmem_get_inode(sb, dir, mode, dev, flags) ramfs_get_inode(sb, dir, mode, dev)
#define shmem_acct_size(flags, size) 0
@@ -4275,7 +4284,7 @@ int shmem_zero_setup(struct vm_area_struct *vma)
if (vma->vm_file)
fput(vma->vm_file);
vma->vm_file = file;
- vma->vm_ops = &shmem_vm_ops;
+ vma->vm_ops = &shmem_anon_vm_ops;

return 0;
}
--
2.38.1.431.g37b22c650d-goog