diff options
| -rw-r--r-- | fs/stack.c | 54 | ||||
| -rw-r--r-- | include/linux/fs_stack.h | 2 |
2 files changed, 52 insertions, 4 deletions
diff --git a/fs/stack.c b/fs/stack.c index 0e20e43ad74..4a6f7f44065 100644 --- a/fs/stack.c +++ b/fs/stack.c @@ -7,10 +7,58 @@ * This function cannot be inlined since i_size_{read,write} is rather * heavy-weight on 32-bit systems */ -void fsstack_copy_inode_size(struct inode *dst, const struct inode *src) +void fsstack_copy_inode_size(struct inode *dst, struct inode *src) { - i_size_write(dst, i_size_read((struct inode *)src)); - dst->i_blocks = src->i_blocks; + loff_t i_size; + blkcnt_t i_blocks; + + /* + * i_size_read() includes its own seqlocking and protection from + * preemption (see include/linux/fs.h): we need nothing extra for + * that here, and prefer to avoid nesting locks than attempt to keep + * i_size and i_blocks in sync together. + */ + i_size = i_size_read(src); + + /* + * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to + * keep the two halves of i_blocks in sync despite SMP or PREEMPT - + * though stat's generic_fillattr() doesn't bother, and we won't be + * applying quotas (where i_blocks does become important) at the + * upper level. + * + * We don't actually know what locking is used at the lower level; + * but if it's a filesystem that supports quotas, it will be using + * i_lock as in inode_add_bytes(). tmpfs uses other locking, and + * its 32-bit is (just) able to exceed 2TB i_size with the aid of + * holes; but its i_blocks cannot carry into the upper long without + * almost 2TB swap - let's ignore that case. + */ + if (sizeof(i_blocks) > sizeof(long)) + spin_lock(&src->i_lock); + i_blocks = src->i_blocks; + if (sizeof(i_blocks) > sizeof(long)) + spin_unlock(&src->i_lock); + + /* + * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for + * fsstack_copy_inode_size() to hold some lock around + * i_size_write(), otherwise i_size_read() may spin forever (see + * include/linux/fs.h). We don't necessarily hold i_mutex when this + * is called, so take i_lock for that case. + * + * And if CONFIG_LBADF (on 32-bit), continue our effort to keep the + * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock + * for that case too, and do both at once by combining the tests. + * + * There is none of this locking overhead in the 64-bit case. + */ + if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long)) + spin_lock(&dst->i_lock); + i_size_write(dst, i_size); + dst->i_blocks = i_blocks; + if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long)) + spin_unlock(&dst->i_lock); } EXPORT_SYMBOL_GPL(fsstack_copy_inode_size); diff --git a/include/linux/fs_stack.h b/include/linux/fs_stack.h index aa60311900d..da317c7163a 100644 --- a/include/linux/fs_stack.h +++ b/include/linux/fs_stack.h @@ -9,7 +9,7 @@ /* externs for fs/stack.c */ extern void fsstack_copy_attr_all(struct inode *dest, const struct inode *src); -extern void fsstack_copy_inode_size(struct inode *dst, const struct inode *src); +extern void fsstack_copy_inode_size(struct inode *dst, struct inode *src); /* inlines */ static inline void fsstack_copy_attr_atime(struct inode *dest, |