[PATCH resubmit] do_mount: reduce stack consumption

From: Heiko Carstens
Date: Fri Nov 04 2005 - 05:52:43 EST

From: Andreas Herrmann <aherrman@xxxxxxxxxx>

This is a resubmit of Andreas' patch that reduces stackframe usage in
do_mount. Problem is that without this patch we get a kernel stack
overflow if we run with 4k stacks (s390 31 bit mode).
See original stack back trace below and Andreas' patch and analysis
here:
http://www.ussg.iu.edu/hypermail/linux/kernel/0410.3/1844.html

<4>Call Trace:
<4>([<000000000014ade6>] buffered_rmqueue+0x36a/0x3b4)
<4> [<000000000014aed6>] __alloc_pages+0xa6/0x350
<4> [<000000000014b258>] __get_free_pages+0x38/0x74
<4> [<000000000014f9fe>] kmem_getpages+0x32/0x140
<4> [<0000000000150396>] cache_alloc_refill+0x3ae/0x58c
<4> [<000000000014feb0>] __kmalloc+0xc0/0xe8
<4> [<00000000002acc64>] zfcp_mempool_alloc+0x24/0x34
<4> [<00000000001494ea>] mempool_alloc+0x56/0x1e8
<4> [<00000000002bfb46>] zfcp_fsf_req_create+0x56/0x5d8
<4> [<00000000002c0cf0>] zfcp_fsf_send_fcp_command_task+0x44/0x5c4
<4> [<00000000002afbda>] zfcp_scsi_command_async+0x7a/0x1f8
<4> [<00000000002afe68>] zfcp_scsi_queuecommand+0x44/0x54
<4> [<000000000024f458>] scsi_dispatch_cmd+0x234/0x3c0
<4> [<0000000000255fb2>] scsi_request_fn+0x2c6/0x67c
<4> [<000000000023f3ea>] __generic_unplug_device+0x52/0x60
<4> [<000000000023d392>] __elv_add_request+0x8a/0x98
<4> [<0000000000240c5e>] __make_request+0x306/0x62c
<4> [<0000000000241074>] generic_make_request+0xf0/0x21c
<4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
<4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
<4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
<4> [<0000000000241074>] generic_make_request+0xf0/0x21c
<4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
<4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
<4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
<4> [<0000000000241074>] generic_make_request+0xf0/0x21c
<4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
<4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
<4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
<4> [<0000000000241074>] generic_make_request+0xf0/0x21c
<4> [<000000000024121a>] submit_bio+0x7a/0x154
<4> [<00000000001736e6>] submit_bh+0x106/0x184
<4> [<000000000017514e>] __block_write_full_page+0x23a/0x58c
<4> [<000000000017558e>] block_write_full_page+0xee/0x108
<4> [<000000000017a908>] blkdev_writepage+0x24/0x38
<4> [<00000000001a0f76>] mpage_writepages+0x1da/0x9d0
<4> [<000000000017a4fa>] generic_writepages+0x22/0x30
<4> [<000000000014cc1e>] do_writepages+0x36/0x54
<4> [<0000000000144fe2>] __filemap_fdatawrite+0x5a/0x6c
<4> [<0000000000145016>] filemap_fdatawrite+0x22/0x30
<4> [<0000000000171244>] sync_blockdev+0x30/0x5c
<4> [<00000000001df074>] journal_recover+0x88/0xbc
<4> [<00000000001e2876>] journal_load+0x52/0xcc
<4> [<00000000001d37b4>] ext3_fill_super+0x1a48/0x1d38
<4> [<0000000000179faa>] get_sb_bdev+0x13a/0x208
<4> [<00000000001d3bd6>] ext3_get_sb+0x22/0x34
<4> [<000000000017a32e>] do_kern_mount+0x86/0x1f4
<4> [<000000000019aaf4>] do_mount+0x1c8/0x8e4
<4> [<000000000019b7ba>] sys_mount+0xce/0x1dc
<4> [<000000000010f9a6>] sysc_do_restart+0xe/0x12

Signed-off-by: Andreas Herrmann <aherrman@xxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---

fs/namespace.c | 80 ++++++++++++++++++++++++++++++++++++---------------------
1 files changed, 51 insertions(+), 29 deletions(-)

diff -urpN linux-2.6/fs/namespace.c linux-2.6-patched/fs/namespace.c
--- linux-2.6/fs/namespace.c 2005-10-28 02:02:08.000000000 +0200
+++ linux-2.6-patched/fs/namespace.c 2005-11-03 13:39:30.000000000 +0100
@@ -619,25 +619,31 @@ out_unlock:
*/
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
- struct nameidata old_nd;
+ struct nameidata *old_nd;
struct vfsmount *mnt = NULL;
int err = mount_is_safe(nd);
if (err)
return err;
if (!old_name || !*old_name)
return -EINVAL;
- err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
- if (err)
+
+ old_nd = kmalloc(sizeof(*old_nd), GFP_KERNEL);
+ if (!old_nd)
+ return -ENOMEM;
+ err = path_lookup(old_name, LOOKUP_FOLLOW, old_nd);
+ if (err) {
+ kfree(old_nd);
return err;
+ }

down_write(&current->namespace->sem);
err = -EINVAL;
- if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {
+ if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd->mnt))) {
err = -ENOMEM;
if (recurse)
- mnt = copy_tree(old_nd.mnt, old_nd.dentry);
+ mnt = copy_tree(old_nd->mnt, old_nd->dentry);
else
- mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
+ mnt = clone_mnt(old_nd->mnt, old_nd->dentry);
}

if (mnt) {
@@ -656,7 +662,8 @@ static int do_loopback(struct nameidata
}

up_write(&current->namespace->sem);
- path_release(&old_nd);
+ path_release(old_nd);
+ kfree(old_nd);
return err;
}

@@ -693,22 +700,29 @@ static int do_remount(struct nameidata *

static int do_move_mount(struct nameidata *nd, char *old_name)
{
- struct nameidata old_nd, parent_nd;
+ struct {
+ struct nameidata old_nd, parent_nd;
+ } *loc;
struct vfsmount *p;
int err = 0;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
- err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
- if (err)
+ loc = kmalloc(sizeof(*loc), GFP_KERNEL);
+ if (!loc)
+ return -ENOMEM;
+ err = path_lookup(old_name, LOOKUP_FOLLOW, &loc->old_nd);
+ if (err) {
+ kfree (loc);
return err;
+ }

down_write(&current->namespace->sem);
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
- if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
+ if (!check_mnt(nd->mnt) || !check_mnt(loc->old_nd.mnt))
goto out;

err = -ENOENT;
@@ -721,28 +735,28 @@ static int do_move_mount(struct nameidat
goto out2;

err = -EINVAL;
- if (old_nd.dentry != old_nd.mnt->mnt_root)
+ if (loc->old_nd.dentry != loc->old_nd.mnt->mnt_root)
goto out2;

- if (old_nd.mnt == old_nd.mnt->mnt_parent)
+ if (loc->old_nd.mnt == loc->old_nd.mnt->mnt_parent)
goto out2;

if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
- S_ISDIR(old_nd.dentry->d_inode->i_mode))
+ S_ISDIR(loc->old_nd.dentry->d_inode->i_mode))
goto out2;

err = -ELOOP;
for (p = nd->mnt; p->mnt_parent!=p; p = p->mnt_parent)
- if (p == old_nd.mnt)
+ if (p == loc->old_nd.mnt)
goto out2;
err = 0;

- detach_mnt(old_nd.mnt, &parent_nd);
- attach_mnt(old_nd.mnt, nd);
+ detach_mnt(loc->old_nd.mnt, &loc->parent_nd);
+ attach_mnt(loc->old_nd.mnt, nd);

/* if the mount is moved, it should no longer be expire
* automatically */
- list_del_init(&old_nd.mnt->mnt_expire);
+ list_del_init(&loc->old_nd.mnt->mnt_expire);
out2:
spin_unlock(&vfsmount_lock);
out1:
@@ -750,8 +764,9 @@ out1:
out:
up_write(&current->namespace->sem);
if (!err)
- path_release(&parent_nd);
- path_release(&old_nd);
+ path_release(&loc->parent_nd);
+ path_release(&loc->old_nd);
+ kfree(loc);
return err;
}

@@ -1014,7 +1029,7 @@ int copy_mount_options(const void __user
long do_mount(char * dev_name, char * dir_name, char *type_page,
unsigned long flags, void *data_page)
{
- struct nameidata nd;
+ struct nameidata *nd;
int retval = 0;
int mnt_flags = 0;

@@ -1041,27 +1056,34 @@ long do_mount(char * dev_name, char * di
mnt_flags |= MNT_NOEXEC;
flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_ACTIVE);

+ nd = kmalloc(sizeof(*nd), GFP_KERNEL);
+ if (!nd)
+ return -ENOMEM;
+
/* ... and get the mountpoint */
- retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
- if (retval)
+ retval = path_lookup(dir_name, LOOKUP_FOLLOW, nd);
+ if (retval) {
+ kfree(nd);
return retval;
+ }

- retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
+ retval = security_sb_mount(dev_name, nd, type_page, flags, data_page);
if (retval)
goto dput_out;

if (flags & MS_REMOUNT)
- retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
+ retval = do_remount(nd, flags & ~MS_REMOUNT, mnt_flags,
data_page);
else if (flags & MS_BIND)
- retval = do_loopback(&nd, dev_name, flags & MS_REC);
+ retval = do_loopback(nd, dev_name, flags & MS_REC);
else if (flags & MS_MOVE)
- retval = do_move_mount(&nd, dev_name);
+ retval = do_move_mount(nd, dev_name);
else
- retval = do_new_mount(&nd, type_page, flags, mnt_flags,
+ retval = do_new_mount(nd, type_page, flags, mnt_flags,
dev_name, data_page);
dput_out:
- path_release(&nd);
+ path_release(nd);
+ kfree(nd);
return retval;
}

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/