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Commit 1b8ab815 authored by Erez Zadok's avatar Erez Zadok Committed by Al Viro
Browse files

VFS/fsstack: handle 32-bit smp + preempt + large files in fsstack_copy_inode_size 



Copy the inode size and blocks from one inode to another correctly on 32-bit
systems with CONFIG_SMP, CONFIG_PREEMPT, or CONFIG_LBDAF.  Use proper inode
spinlocks only when i_size/i_blocks cannot fit in one 32-bit word.

Signed-off-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: default avatarErez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 9afa2fb6

fs/stack.c

+51 −3
Original line number Diff line number Diff line
@@ -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);

include/linux/fs_stack.h

+1 −1
Original line number Diff line number Diff line
@@ -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,