[PATCH 03/10] mm: convert i_mmap_mutex to rwsem

From: Davidlohr Bueso
Date: Fri Oct 24 2014 - 18:06:55 EST

The i_mmap_mutex is a close cousin of the anon vma lock,
both protecting similar data, one for file backed pages
and the other for anon memory. To this end, this lock can
also be a rwsem. In addition, there are some important
opportunities to share the lock when there are no tree
modifications.

This conversion is straightforward. For now, all users take
the write lock.

Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 10 +++++-----
fs/inode.c | 2 +-
include/linux/fs.h | 7 ++++---
include/linux/mmu_notifier.h | 2 +-
kernel/events/uprobes.c | 2 +-
mm/filemap.c | 10 +++++-----
mm/fremap.c | 4 ++--
mm/hugetlb.c | 10 +++++-----
mm/mmap.c | 8 ++++----
mm/mremap.c | 2 +-
mm/rmap.c | 6 +++---
11 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index a082709..5eba47f 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -472,12 +472,12 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
}

/*
- * Hugetlbfs is not reclaimable; therefore its i_mmap_mutex will never
+ * Hugetlbfs is not reclaimable; therefore its i_mmap_rwsem will never
* be taken from reclaim -- unlike regular filesystems. This needs an
* annotation because huge_pmd_share() does an allocation under
- * i_mmap_mutex.
+ * i_mmap_rwsem.
*/
-static struct lock_class_key hugetlbfs_i_mmap_mutex_key;
+static struct lock_class_key hugetlbfs_i_mmap_rwsem_key;

static struct inode *hugetlbfs_get_inode(struct super_block *sb,
struct inode *dir,
@@ -495,8 +495,8 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
struct hugetlbfs_inode_info *info;
inode->i_ino = get_next_ino();
inode_init_owner(inode, dir, mode);
- lockdep_set_class(&inode->i_mapping->i_mmap_mutex,
- &hugetlbfs_i_mmap_mutex_key);
+ lockdep_set_class(&inode->i_mapping->i_mmap_rwsem,
+ &hugetlbfs_i_mmap_rwsem_key);
inode->i_mapping->a_ops = &hugetlbfs_aops;
inode->i_mapping->backing_dev_info =&hugetlbfs_backing_dev_info;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
diff --git a/fs/inode.c b/fs/inode.c
index 26753ba..1732d6b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -349,7 +349,7 @@ void address_space_init_once(struct address_space *mapping)
memset(mapping, 0, sizeof(*mapping));
INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
spin_lock_init(&mapping->tree_lock);
- mutex_init(&mapping->i_mmap_mutex);
+ init_rwsem(&mapping->i_mmap_rwsem);
INIT_LIST_HEAD(&mapping->private_list);
spin_lock_init(&mapping->private_lock);
mapping->i_mmap = RB_ROOT;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 042d5c6..b183792 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -18,6 +18,7 @@
#include <linux/pid.h>
#include <linux/bug.h>
#include <linux/mutex.h>
+#include <linux/rwsem.h>
#include <linux/capability.h>
#include <linux/semaphore.h>
#include <linux/fiemap.h>
@@ -388,7 +389,7 @@ struct address_space {
atomic_t i_mmap_writable;/* count VM_SHARED mappings */
struct rb_root i_mmap; /* tree of private and shared mappings */
struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
- struct mutex i_mmap_mutex; /* protect tree, count, list */
+ struct rw_semaphore i_mmap_rwsem; /* protect tree, count, list */
/* Protected by tree_lock together with the radix tree */
unsigned long nrpages; /* number of total pages */
unsigned long nrshadows; /* number of shadow entries */
@@ -456,12 +457,12 @@ int mapping_tagged(struct address_space *mapping, int tag);

static inline void i_mmap_lock_write(struct address_space *mapping)
{
- mutex_lock(&mapping->i_mmap_mutex);
+ down_write(&mapping->i_mmap_rwsem);
}

static inline void i_mmap_unlock_write(struct address_space *mapping)
{
- mutex_unlock(&mapping->i_mmap_mutex);
+ up_write(&mapping->i_mmap_rwsem);
}

/*
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 88787bb..ab8564b 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -154,7 +154,7 @@ struct mmu_notifier_ops {
* Therefore notifier chains can only be traversed when either
*
* 1. mmap_sem is held.
- * 2. One of the reverse map locks is held (i_mmap_mutex or anon_vma->rwsem).
+ * 2. One of the reverse map locks is held (i_mmap_rwsem or anon_vma->rwsem).
* 3. No other concurrent thread can access the list (release)
*/
struct mmu_notifier {
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d246a0a..045b649 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -731,7 +731,7 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)

if (!prev && !more) {
/*
- * Needs GFP_NOWAIT to avoid i_mmap_mutex recursion through
+ * Needs GFP_NOWAIT to avoid i_mmap_rwsem recursion through
* reclaim. This is optimistic, no harm done if it fails.
*/
prev = kmalloc(sizeof(struct map_info),
diff --git a/mm/filemap.c b/mm/filemap.c
index 14b4642..e8905bc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -62,16 +62,16 @@
/*
* Lock ordering:
*
- * ->i_mmap_mutex (truncate_pagecache)
+ * ->i_mmap_rwsem (truncate_pagecache)
* ->private_lock (__free_pte->__set_page_dirty_buffers)
* ->swap_lock (exclusive_swap_page, others)
* ->mapping->tree_lock
*
* ->i_mutex
- * ->i_mmap_mutex (truncate->unmap_mapping_range)
+ * ->i_mmap_rwsem (truncate->unmap_mapping_range)
*
* ->mmap_sem
- * ->i_mmap_mutex
+ * ->i_mmap_rwsem
* ->page_table_lock or pte_lock (various, mainly in memory.c)
* ->mapping->tree_lock (arch-dependent flush_dcache_mmap_lock)
*
@@ -85,7 +85,7 @@
* sb_lock (fs/fs-writeback.c)
* ->mapping->tree_lock (__sync_single_inode)
*
- * ->i_mmap_mutex
+ * ->i_mmap_rwsem
* ->anon_vma.lock (vma_adjust)
*
* ->anon_vma.lock
@@ -105,7 +105,7 @@
* ->inode->i_lock (zap_pte_range->set_page_dirty)
* ->private_lock (zap_pte_range->__set_page_dirty_buffers)
*
- * ->i_mmap_mutex
+ * ->i_mmap_rwsem
* ->tasklist_lock (memory_failure, collect_procs_ao)
*/

diff --git a/mm/fremap.c b/mm/fremap.c
index 72b8fa3..11ef7ec 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -238,13 +238,13 @@ get_write_lock:
}
goto out_freed;
}
- mutex_lock(&mapping->i_mmap_mutex);
+ i_mmap_lock_write(mapping);
flush_dcache_mmap_lock(mapping);
vma->vm_flags |= VM_NONLINEAR;
vma_interval_tree_remove(vma, &mapping->i_mmap);
vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
flush_dcache_mmap_unlock(mapping);
- mutex_unlock(&mapping->i_mmap_mutex);
+ i_mmap_unlock_write(mapping);
}

if (vma->vm_flags & VM_LOCKED) {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fa86464..7eeab54 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2724,9 +2724,9 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb,
* on its way out. We're lucky that the flag has such an appropriate
* name, and can in fact be safely cleared here. We could clear it
* before the __unmap_hugepage_range above, but all that's necessary
- * is to clear it before releasing the i_mmap_mutex. This works
+ * is to clear it before releasing the i_mmap_rwsem. This works
* because in the context this is called, the VMA is about to be
- * destroyed and the i_mmap_mutex is held.
+ * destroyed and the i_mmap_rwsem is held.
*/
vma->vm_flags &= ~VM_MAYSHARE;
}
@@ -3368,9 +3368,9 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
spin_unlock(ptl);
}
/*
- * Must flush TLB before releasing i_mmap_mutex: x86's huge_pmd_unshare
+ * Must flush TLB before releasing i_mmap_rwsem: x86's huge_pmd_unshare
* may have cleared our pud entry and done put_page on the page table:
- * once we release i_mmap_mutex, another task can do the final put_page
+ * once we release i_mmap_rwsem, another task can do the final put_page
* and that page table be reused and filled with junk.
*/
flush_tlb_range(vma, start, end);
@@ -3523,7 +3523,7 @@ static int vma_shareable(struct vm_area_struct *vma, unsigned long addr)
* and returns the corresponding pte. While this is not necessary for the
* !shared pmd case because we can allocate the pmd later as well, it makes the
* code much cleaner. pmd allocation is essential for the shared case because
- * pud has to be populated inside the same i_mmap_mutex section - otherwise
+ * pud has to be populated inside the same i_mmap_rwsem section - otherwise
* racing tasks could either miss the sharing (see huge_pte_offset) or select a
* bad pmd for sharing.
*/
diff --git a/mm/mmap.c b/mm/mmap.c
index ac4d05a..06c5b2b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -232,7 +232,7 @@ error:
}

/*
- * Requires inode->i_mapping->i_mmap_mutex
+ * Requires inode->i_mapping->i_mmap_rwsem
*/
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
struct file *file, struct address_space *mapping)
@@ -2785,7 +2785,7 @@ void exit_mmap(struct mm_struct *mm)

/* Insert vm structure into process list sorted by address
* and into the inode's i_mmap tree. If vm_file is non-NULL
- * then i_mmap_mutex is taken here.
+ * then i_mmap_rwsem is taken here.
*/
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
@@ -3080,7 +3080,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
*/
if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
BUG();
- mutex_lock_nest_lock(&mapping->i_mmap_mutex, &mm->mmap_sem);
+ down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_sem);
}
}

@@ -3107,7 +3107,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
* vma in this mm is backed by the same anon_vma or address_space.
*
* We can take all the locks in random order because the VM code
- * taking i_mmap_mutex or anon_vma->rwsem outside the mmap_sem never
+ * taking i_mmap_rwsem or anon_vma->rwsem outside the mmap_sem never
* takes more than one of them in a row. Secondly we're protected
* against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
*
diff --git a/mm/mremap.c b/mm/mremap.c
index 426b448..84aa36f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -99,7 +99,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
spinlock_t *old_ptl, *new_ptl;

/*
- * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
+ * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
* locks to ensure that rmap will always observe either the old or the
* new ptes. This is the easiest way to avoid races with
* truncate_pagecache(), page migration, etc...
diff --git a/mm/rmap.c b/mm/rmap.c
index 46fe32a..f234bc6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -23,7 +23,7 @@
* inode->i_mutex (while writing or truncating, not reading or faulting)
* mm->mmap_sem
* page->flags PG_locked (lock_page)
- * mapping->i_mmap_mutex
+ * mapping->i_mmap_rwsem
* anon_vma->rwsem
* mm->page_table_lock or pte_lock
* zone->lru_lock (in mark_page_accessed, isolate_lru_page)
@@ -1244,7 +1244,7 @@ out_mlock:
/*
* We need mmap_sem locking, Otherwise VM_LOCKED check makes
* unstable result and race. Plus, We can't wait here because
- * we now hold anon_vma->rwsem or mapping->i_mmap_mutex.
+ * we now hold anon_vma->rwsem or mapping->i_mmap_rwsem.
* if trylock failed, the page remain in evictable lru and later
* vmscan could retry to move the page to unevictable lru if the
* page is actually mlocked.
@@ -1668,7 +1668,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
* The page lock not only makes sure that page->mapping cannot
* suddenly be NULLified by truncation, it makes sure that the
* structure at mapping cannot be freed and reused yet,
- * so we can safely take mapping->i_mmap_mutex.
+ * so we can safely take mapping->i_mmap_rwsem.
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);

--
1.8.4.5

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