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Commit a02f76c3 authored by Al Viro's avatar Al Viro
Browse files

[PATCH] get stack footprint of pathname resolution back to relative sanity 



Somebody had put struct nameidata in stack frame of link_path_walk().
Unfortunately, there are certain realities to deal with:
	* It's in the middle of recursion.  Depth is equal to the nesting
depth of symlinks, i.e. up to 8.
	* struct namiedata is, even if one discards the intent junk,
at least 12 pointers + 5 ints.
	* moreover, adding a stack frame is not free in that situation.
	* there are fs methods called on top of that, and they also have
stack footprint.
	* kernel stack is not infinite.

The thing is, even if one chooses to deal with -ESTALE that way (and it's
one hell of an overkill), the only thing that needs to be preserved is
vfsmount + dentry, not the entire struct nameidata.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent b4d232e6

fs/namei.c

+32 −31
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ 
 * any extra contention...

 */



static int link_path_walk(const char *name, struct nameidata *nd);

static int __link_path_walk(const char *name, struct nameidata *nd);



/* In order to reduce some races, while at the same time doing additional

 * checking and hopefully speeding things up, we copy filenames to the
@@ -563,6 +563,37 @@ walk_init_root(const char *name, struct nameidata *nd) 
	return 1;

}



/*

 * Wrapper to retry pathname resolution whenever the underlying

 * file system returns an ESTALE.

 *

 * Retry the whole path once, forcing real lookup requests

 * instead of relying on the dcache.

 */

static __always_inline int link_path_walk(const char *name, struct nameidata *nd)

{

	struct path save = nd->path;

	int result;



	/* make sure the stuff we saved doesn't go away */

	dget(save.dentry);

	mntget(save.mnt);



	result = __link_path_walk(name, nd);

	if (result == -ESTALE) {

		/* nd->path had been dropped */

		nd->path = save;

		dget(nd->path.dentry);

		mntget(nd->path.mnt);

		nd->flags |= LOOKUP_REVAL;

		result = __link_path_walk(name, nd);

	}



	path_put(&save);



	return result;

}



static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link)

{

	int res = 0;
@@ -1020,36 +1051,6 @@ return_err: 
	return err;

}



/*

 * Wrapper to retry pathname resolution whenever the underlying

 * file system returns an ESTALE.

 *

 * Retry the whole path once, forcing real lookup requests

 * instead of relying on the dcache.

 */

static int link_path_walk(const char *name, struct nameidata *nd)

{

	struct nameidata save = *nd;

	int result;



	/* make sure the stuff we saved doesn't go away */

	dget(save.path.dentry);

	mntget(save.path.mnt);



	result = __link_path_walk(name, nd);

	if (result == -ESTALE) {

		*nd = save;

		dget(nd->path.dentry);

		mntget(nd->path.mnt);

		nd->flags |= LOOKUP_REVAL;

		result = __link_path_walk(name, nd);

	}



	path_put(&save.path);



	return result;

}



static int path_walk(const char *name, struct nameidata *nd)

{

	current->total_link_count = 0;