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Subject[PATCH 4/4] staging: lustre: obd_mount: fix possible race with module unload.
lustre_fill_super() calls client_fill_super() without holding a
reference to the module containing client_fill_super. If that
module is unloaded at a bad time, this can crash.

To be able to get a reference to the module using
try_get_module(), we need a pointer to the module.

So replace
lustre_register_client_fill_super() and
lustre_register_kill_super_cb()
with a single
lustre_register_super_ops()
which also passed a module pointer.

Then use a spinlock to ensure the module pointer isn't removed
while try_module_get() is running, and use try_module_get() to
ensure we have a reference before calling client_fill_super().

Signed-off-by: NeilBrown <neilb@suse.com>
---
.../staging/lustre/lustre/include/lustre_disk.h | 5 ++-
drivers/staging/lustre/lustre/llite/super25.c | 6 +---
drivers/staging/lustre/lustre/obdclass/obd_mount.c | 30 +++++++++++++-------
3 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/drivers/staging/lustre/lustre/include/lustre_disk.h b/drivers/staging/lustre/lustre/include/lustre_disk.h
index 5089ec02dcad..100e993ab00b 100644
--- a/drivers/staging/lustre/lustre/include/lustre_disk.h
+++ b/drivers/staging/lustre/lustre/include/lustre_disk.h
@@ -141,8 +141,9 @@ struct lustre_sb_info {
/* obd_mount.c */

int lustre_start_mgc(struct super_block *sb);
-void lustre_register_client_fill_super(int (*cfs)(struct super_block *sb));
-void lustre_register_kill_super_cb(void (*cfs)(struct super_block *sb));
+void lustre_register_super_ops(struct module *mod,
+ int (*cfs)(struct super_block *sb),
+ void (*ksc)(struct super_block *sb));
int lustre_common_put_super(struct super_block *sb);

int mgc_fsname2resid(char *fsname, struct ldlm_res_id *res_id, int type);
diff --git a/drivers/staging/lustre/lustre/llite/super25.c b/drivers/staging/lustre/lustre/llite/super25.c
index 0bda111a096e..10105339790e 100644
--- a/drivers/staging/lustre/lustre/llite/super25.c
+++ b/drivers/staging/lustre/lustre/llite/super25.c
@@ -159,8 +159,7 @@ static int __init lustre_init(void)
if (rc != 0)
goto out_inode_fini_env;

- lustre_register_client_fill_super(ll_fill_super);
- lustre_register_kill_super_cb(ll_kill_super);
+ lustre_register_super_ops(THIS_MODULE, ll_fill_super, ll_kill_super);
lustre_register_client_process_config(ll_process_config);

return 0;
@@ -181,8 +180,7 @@ static int __init lustre_init(void)

static void __exit lustre_exit(void)
{
- lustre_register_client_fill_super(NULL);
- lustre_register_kill_super_cb(NULL);
+ lustre_register_super_ops(NULL, NULL, NULL);
lustre_register_client_process_config(NULL);

debugfs_remove(llite_root);
diff --git a/drivers/staging/lustre/lustre/obdclass/obd_mount.c b/drivers/staging/lustre/lustre/obdclass/obd_mount.c
index 8068cbbc8390..acc1ea773c9c 100644
--- a/drivers/staging/lustre/lustre/obdclass/obd_mount.c
+++ b/drivers/staging/lustre/lustre/obdclass/obd_mount.c
@@ -49,8 +49,9 @@
#include <lustre_disk.h>
#include <uapi/linux/lustre/lustre_param.h>

+static DEFINE_SPINLOCK(client_lock);
+static struct module *client_mod;
static int (*client_fill_super)(struct super_block *sb);
-
static void (*kill_super_cb)(struct super_block *sb);

/**************** config llog ********************/
@@ -1143,10 +1144,15 @@ static int lustre_fill_super(struct super_block *sb, void *lmd2_data, int silent
}

if (lmd_is_client(lmd)) {
+ bool have_client = false;
CDEBUG(D_MOUNT, "Mounting client %s\n", lmd->lmd_profile);
if (!client_fill_super)
request_module("lustre");
- if (!client_fill_super) {
+ spin_lock(&client_lock);
+ if (client_fill_super && try_module_get(client_mod))
+ have_client = true;
+ spin_unlock(&client_lock);
+ if (!have_client) {
LCONSOLE_ERROR_MSG(0x165, "Nothing registered for client mount! Is the 'lustre' module loaded?\n");
lustre_put_lsi(sb);
rc = -ENODEV;
@@ -1159,7 +1165,9 @@ static int lustre_fill_super(struct super_block *sb, void *lmd2_data, int silent
/* Connect and start */
/* (should always be ll_fill_super) */
rc = (*client_fill_super)(sb);
- /* c_f_s will call lustre_common_put_super on failure */
+ /* c_f_s will call lustre_common_put_super on failure, otherwise
+ * c_f_s will have taken another reference to the module */
+ module_put(client_mod);
}
} else {
CERROR("This is client-side-only module, cannot handle server mount.\n");
@@ -1185,17 +1193,17 @@ static int lustre_fill_super(struct super_block *sb, void *lmd2_data, int silent
/* We can't call ll_fill_super by name because it lives in a module that
* must be loaded after this one.
*/
-void lustre_register_client_fill_super(int (*cfs)(struct super_block *sb))
+void lustre_register_super_ops(struct module *mod,
+ int (*cfs)(struct super_block *sb),
+ void (*ksc)(struct super_block *sb))
{
+ spin_lock(&client_lock);
+ client_mod = mod;
client_fill_super = cfs;
+ kill_super_cb = ksc;
+ spin_unlock(&client_lock);
}
-EXPORT_SYMBOL(lustre_register_client_fill_super);
-
-void lustre_register_kill_super_cb(void (*cfs)(struct super_block *sb))
-{
- kill_super_cb = cfs;
-}
-EXPORT_SYMBOL(lustre_register_kill_super_cb);
+EXPORT_SYMBOL(lustre_register_super_ops);

/***************** FS registration ******************/
static struct dentry *lustre_mount(struct file_system_type *fs_type, int flags,

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