diff options
| -rw-r--r-- | include/linux/mm.h | 3 | ||||
| -rw-r--r-- | include/linux/pagemap.h | 1 | ||||
| -rw-r--r-- | include/linux/rmap.h | 8 | ||||
| -rw-r--r-- | mm/mmap.c | 158 |
4 files changed, 170 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 6e695ea..866a3db 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1104,6 +1104,9 @@ extern struct vm_area_struct *copy_vma(struct vm_area_struct **, unsigned long addr, unsigned long len, pgoff_t pgoff); extern void exit_mmap(struct mm_struct *); +extern int mm_take_all_locks(struct mm_struct *mm); +extern void mm_drop_all_locks(struct mm_struct *mm); + #ifdef CONFIG_PROC_FS /* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */ extern void added_exe_file_vma(struct mm_struct *mm); diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index a81d818..a39b38c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -20,6 +20,7 @@ */ #define AS_EIO (__GFP_BITS_SHIFT + 0) /* IO error on async write */ #define AS_ENOSPC (__GFP_BITS_SHIFT + 1) /* ENOSPC on async write */ +#define AS_MM_ALL_LOCKS (__GFP_BITS_SHIFT + 2) /* under mm_take_all_locks() */ static inline void mapping_set_error(struct address_space *mapping, int error) { diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 1383692..69407f8 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -26,6 +26,14 @@ */ struct anon_vma { spinlock_t lock; /* Serialize access to vma list */ + /* + * NOTE: the LSB of the head.next is set by + * mm_take_all_locks() _after_ taking the above lock. So the + * head must only be read/written after taking the above lock + * to be sure to see a valid next pointer. The LSB bit itself + * is serialized by a system wide lock only visible to + * mm_take_all_locks() (mm_all_locks_mutex). + */ struct list_head head; /* List of private "related" vmas */ }; @@ -2268,3 +2268,161 @@ int install_special_mapping(struct mm_struct *mm, return 0; } + +static DEFINE_MUTEX(mm_all_locks_mutex); + +static void vm_lock_anon_vma(struct anon_vma *anon_vma) +{ + if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) { + /* + * The LSB of head.next can't change from under us + * because we hold the mm_all_locks_mutex. + */ + spin_lock(&anon_vma->lock); + /* + * We can safely modify head.next after taking the + * anon_vma->lock. If some other vma in this mm shares + * the same anon_vma we won't take it again. + * + * No need of atomic instructions here, head.next + * can't change from under us thanks to the + * anon_vma->lock. + */ + if (__test_and_set_bit(0, (unsigned long *) + &anon_vma->head.next)) + BUG(); + } +} + +static void vm_lock_mapping(struct address_space *mapping) +{ + if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) { + /* + * AS_MM_ALL_LOCKS can't change from under us because + * we hold the mm_all_locks_mutex. + * + * Operations on ->flags have to be atomic because + * even if AS_MM_ALL_LOCKS is stable thanks to the + * mm_all_locks_mutex, there may be other cpus + * changing other bitflags in parallel to us. + */ + if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags)) + BUG(); + spin_lock(&mapping->i_mmap_lock); + } +} + +/* + * This operation locks against the VM for all pte/vma/mm related + * operations that could ever happen on a certain mm. This includes + * vmtruncate, try_to_unmap, and all page faults. + * + * The caller must take the mmap_sem in write mode before calling + * mm_take_all_locks(). The caller isn't allowed to release the + * mmap_sem until mm_drop_all_locks() returns. + * + * mmap_sem in write mode is required in order to block all operations + * that could modify pagetables and free pages without need of + * altering the vma layout (for example populate_range() with + * nonlinear vmas). It's also needed in write mode to avoid new + * anon_vmas to be associated with existing vmas. + * + * A single task can't take more than one mm_take_all_locks() in a row + * or it would deadlock. + * + * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in + * mapping->flags avoid to take the same lock twice, if more than one + * 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_lock or anon_vma->lock 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. + * + * mm_take_all_locks() and mm_drop_all_locks are expensive operations + * that may have to take thousand of locks. + * + * mm_take_all_locks() can fail if it's interrupted by signals. + */ +int mm_take_all_locks(struct mm_struct *mm) +{ + struct vm_area_struct *vma; + int ret = -EINTR; + + BUG_ON(down_read_trylock(&mm->mmap_sem)); + + mutex_lock(&mm_all_locks_mutex); + + for (vma = mm->mmap; vma; vma = vma->vm_next) { + if (signal_pending(current)) + goto out_unlock; + if (vma->anon_vma) + vm_lock_anon_vma(vma->anon_vma); + if (vma->vm_file && vma->vm_file->f_mapping) + vm_lock_mapping(vma->vm_file->f_mapping); + } + ret = 0; + +out_unlock: + if (ret) + mm_drop_all_locks(mm); + + return ret; +} + +static void vm_unlock_anon_vma(struct anon_vma *anon_vma) +{ + if (test_bit(0, (unsigned long *) &anon_vma->head.next)) { + /* + * The LSB of head.next can't change to 0 from under + * us because we hold the mm_all_locks_mutex. + * + * We must however clear the bitflag before unlocking + * the vma so the users using the anon_vma->head will + * never see our bitflag. + * + * No need of atomic instructions here, head.next + * can't change from under us until we release the + * anon_vma->lock. + */ + if (!__test_and_clear_bit(0, (unsigned long *) + &anon_vma->head.next)) + BUG(); + spin_unlock(&anon_vma->lock); + } +} + +static void vm_unlock_mapping(struct address_space *mapping) +{ + if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) { + /* + * AS_MM_ALL_LOCKS can't change to 0 from under us + * because we hold the mm_all_locks_mutex. + */ + spin_unlock(&mapping->i_mmap_lock); + if (!test_and_clear_bit(AS_MM_ALL_LOCKS, + &mapping->flags)) + BUG(); + } +} + +/* + * The mmap_sem cannot be released by the caller until + * mm_drop_all_locks() returns. + */ +void mm_drop_all_locks(struct mm_struct *mm) +{ + struct vm_area_struct *vma; + + BUG_ON(down_read_trylock(&mm->mmap_sem)); + BUG_ON(!mutex_is_locked(&mm_all_locks_mutex)); + + for (vma = mm->mmap; vma; vma = vma->vm_next) { + if (vma->anon_vma) + vm_unlock_anon_vma(vma->anon_vma); + if (vma->vm_file && vma->vm_file->f_mapping) + vm_unlock_mapping(vma->vm_file->f_mapping); + } + + mutex_unlock(&mm_all_locks_mutex); +} |
