Ocfs2 devel - Feb 2014 - [PATCH] ocfs2: dlm: fix lock migration crash

This issue was introduced by commit 800deef3 where it replaced list_for_each
with list_for_each_entry. The variable "lock" will point to invalid
data if
"tmpq" list is empty and a panic will be triggered due to this.
Sunil advised reverting it back, but the old version was also not right. At
the end of the outer for loop, that list_for_each_entry will also set
"lock"
to an invalid data, then in the next loop, if the "tmpq" list is
empty, "lock"
will be an stale invalid data and cause the panic. So reverting the
list_for_each
back and reset "lock" to NULL to fix this issue.

Another concern is that this seemes can not happen because the "tmpq"
list should
not be empty. Let me describe how.
old lock resource owner(node 1):                                  migratation
target(node 2):
image there's lockres with a EX lock from node 2 in
granted list, a NR lock from node x with convert_type
EX in converting list.
dlm_empty_lockres() {
 dlm_pick_migration_target() {
   pick node 2 as target as its lock is the first one
   in granted list.
 }
 dlm_migrate_lockres() {
   dlm_mark_lockres_migrating() {
     res->state |= DLM_LOCK_RES_BLOCK_DIRTY;
     wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
	 //after the above code, we can not dirty lockres any more,
     // so dlm_thread shuffle list will not run
                                                                   downconvert
lock from EX to NR
                                                                   upconvert
lock from NR to EX
<<< migration may schedule out here, then
<<< node 2 send down convert request to convert type from EX to
<<< NR, then send up convert request to convert type from NR to
<<< EX, at this time, lockres granted list is empty, and two locks
<<< in the converting list, node x up convert lock followed by
<<< node 2 up convert lock.

	 // will set lockres RES_MIGRATING flag, the following
	 // lock/unlock can not run
     dlm_lockres_release_ast(dlm, res);
   }

   dlm_send_one_lockres()
                                                                
dlm_process_recovery_data()
                                                                   for (i=0;
i<mres->num_locks; i++)
                                                                     if
(ml->node == dlm->node_num)
                                                                       for (j =
DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
                                                                       
list_for_each_entry(lock, tmpq, list)
                                                                        if
(lock) break; <<< lock is invalid as grant list is empty.
                                                                       }
                                                                       if
(lock->ml.node != ml->node)
                                                                         BUG()
>>> crash here
 }
I see the above locks status from a vmcore of our internal bug.

Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
Cc: Sunil Mushran <sunil.mushran at gmail.com>
Cc: Srinivas Eeda <srinivas.eeda at oracle.com>
Cc: <stable at vger.kernel.org>
---
 fs/ocfs2/dlm/dlmrecovery.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index 7035af0..c2dd258 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1750,13 +1750,13 @@ static int dlm_process_recovery_data(struct dlm_ctxt
*dlm,
 				     struct dlm_migratable_lockres *mres)
 {
 	struct dlm_migratable_lock *ml;
-	struct list_head *queue;
+	struct list_head *queue, *iter;
 	struct list_head *tmpq = NULL;
 	struct dlm_lock *newlock = NULL;
 	struct dlm_lockstatus *lksb = NULL;
 	int ret = 0;
 	int i, j, bad;
-	struct dlm_lock *lock = NULL;
+	struct dlm_lock *lock;
 	u8 from = O2NM_MAX_NODES;
 	unsigned int added = 0;
 	__be64 c;
@@ -1791,14 +1791,16 @@ static int dlm_process_recovery_data(struct dlm_ctxt
*dlm,
 			/* MIGRATION ONLY! */
 			BUG_ON(!(mres->flags & DLM_MRES_MIGRATION));
 
+			lock = NULL;
 			spin_lock(&res->spinlock);
 			for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
 				tmpq = dlm_list_idx_to_ptr(res, j);
-				list_for_each_entry(lock, tmpq, list) {
-					if (lock->ml.cookie != ml->cookie)
-						lock = NULL;
-					else
+				list_for_each(iter, tmpq) {
+					lock = list_entry(iter,
+						  struct dlm_lock, list);
+					if (lock->ml.cookie == ml->cookie)
 						break;
+					lock = NULL;
 				}
 				if (lock)
 					break;
-- 
1.7.9.5

reviewed-by Wengang Wang <wen.gang.wang at oracle.com>

? 2014?02?26? 15:47, Junxiao Bi ??:
> This issue was introduced by commit 800deef3 where it replaced
list_for_each
> with list_for_each_entry. The variable "lock" will point to
invalid data if
> "tmpq" list is empty and a panic will be triggered due to this.
> Sunil advised reverting it back, but the old version was also not right. At
> the end of the outer for loop, that list_for_each_entry will also set
"lock"
> to an invalid data, then in the next loop, if the "tmpq" list is
empty, "lock"
> will be an stale invalid data and cause the panic. So reverting the
list_for_each
> back and reset "lock" to NULL to fix this issue.
>
> Another concern is that this seemes can not happen because the
"tmpq" list should
> not be empty. Let me describe how.
> old lock resource owner(node 1):                                 
migratation target(node 2):
> image there's lockres with a EX lock from node 2 in
> granted list, a NR lock from node x with convert_type
> EX in converting list.
> dlm_empty_lockres() {
>   dlm_pick_migration_target() {
>     pick node 2 as target as its lock is the first one
>     in granted list.
>   }
>   dlm_migrate_lockres() {
>     dlm_mark_lockres_migrating() {
>       res->state |= DLM_LOCK_RES_BLOCK_DIRTY;
>       wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
> 	 //after the above code, we can not dirty lockres any more,
>       // so dlm_thread shuffle list will not run
>                                                                    
downconvert lock from EX to NR
>                                                                    
upconvert lock from NR to EX
> <<< migration may schedule out here, then
> <<< node 2 send down convert request to convert type from EX to
> <<< NR, then send up convert request to convert type from NR to
> <<< EX, at this time, lockres granted list is empty, and two locks
> <<< in the converting list, node x up convert lock followed by
> <<< node 2 up convert lock.
>
> 	 // will set lockres RES_MIGRATING flag, the following
> 	 // lock/unlock can not run
>       dlm_lockres_release_ast(dlm, res);
>     }
>
>     dlm_send_one_lockres()
>                                                                  
dlm_process_recovery_data()
>                                                                     for
(i=0; i<mres->num_locks; i++)
>                                                                       if
(ml->node == dlm->node_num)
>                                                                         for
(j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
>                                                                         
list_for_each_entry(lock, tmpq, list)
>                                                                          if
(lock) break; <<< lock is invalid as grant list is empty.
>                                                                         }
>                                                                         if
(lock->ml.node != ml->node)
>                                                                          
BUG() >>> crash here
>   }
> I see the above locks status from a vmcore of our internal bug.
>
> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
> Cc: Sunil Mushran <sunil.mushran at gmail.com>
> Cc: Srinivas Eeda <srinivas.eeda at oracle.com>
> Cc: <stable at vger.kernel.org>
> ---
>   fs/ocfs2/dlm/dlmrecovery.c |   14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index 7035af0..c2dd258 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1750,13 +1750,13 @@ static int dlm_process_recovery_data(struct
dlm_ctxt *dlm,
>   				     struct dlm_migratable_lockres *mres)
>   {
>   	struct dlm_migratable_lock *ml;
> -	struct list_head *queue;
> +	struct list_head *queue, *iter;
>   	struct list_head *tmpq = NULL;
>   	struct dlm_lock *newlock = NULL;
>   	struct dlm_lockstatus *lksb = NULL;
>   	int ret = 0;
>   	int i, j, bad;
> -	struct dlm_lock *lock = NULL;
> +	struct dlm_lock *lock;
>   	u8 from = O2NM_MAX_NODES;
>   	unsigned int added = 0;
>   	__be64 c;
> @@ -1791,14 +1791,16 @@ static int dlm_process_recovery_data(struct
dlm_ctxt *dlm,
>   			/* MIGRATION ONLY! */
>   			BUG_ON(!(mres->flags & DLM_MRES_MIGRATION));
>   
> +			lock = NULL;
>   			spin_lock(&res->spinlock);
>   			for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
>   				tmpq = dlm_list_idx_to_ptr(res, j);
> -				list_for_each_entry(lock, tmpq, list) {
> -					if (lock->ml.cookie != ml->cookie)
> -						lock = NULL;
> -					else
> +				list_for_each(iter, tmpq) {
> +					lock = list_entry(iter,
> +						  struct dlm_lock, list);
> +					if (lock->ml.cookie == ml->cookie)
>   						break;
> +					lock = NULL;
>   				}
>   				if (lock)
>   					break;

On Wed, 26 Feb 2014 15:47:37 +0800 Junxiao Bi <junxiao.bi at oracle.com>
wrote:
> This issue was introduced by commit 800deef3 where it replaced
list_for_each
> with list_for_each_entry. The variable "lock" will point to
invalid data if
> "tmpq" list is empty and a panic will be triggered due to this.
> Sunil advised reverting it back, but the old version was also not right. At
> the end of the outer for loop, that list_for_each_entry will also set
"lock"
> to an invalid data, then in the next loop, if the "tmpq" list is
empty, "lock"
> will be an stale invalid data and cause the panic. So reverting the
list_for_each
> back and reset "lock" to NULL to fix this issue.
> 
> ...
>
> Cc: <stable at vger.kernel.org>
800deef3 was back in 2007, so this doesn't seem a terribly urgent bugfix!

I think what I'll do is to target 3.15-rc1 to give people time to
review and test this.  But I'll retain the cc:stable so the fix gets
backported into 3.14.x and earlier kernels.

OK?

looks good, thanks Junxiao for fixing this.

Reviewed-by: Srinivas Eeda<srinivas.eeda at oracle.com>

On 02/25/2014 11:47 PM, Junxiao Bi wrote:
> This issue was introduced by commit 800deef3 where it replaced
list_for_each
> with list_for_each_entry. The variable "lock" will point to
invalid data if
> "tmpq" list is empty and a panic will be triggered due to this.
> Sunil advised reverting it back, but the old version was also not right. At
> the end of the outer for loop, that list_for_each_entry will also set
"lock"
> to an invalid data, then in the next loop, if the "tmpq" list is
empty, "lock"
> will be an stale invalid data and cause the panic. So reverting the
list_for_each
> back and reset "lock" to NULL to fix this issue.
>
> Another concern is that this seemes can not happen because the
"tmpq" list should
> not be empty. Let me describe how.
> old lock resource owner(node 1):                                 
migratation target(node 2):
> image there's lockres with a EX lock from node 2 in
> granted list, a NR lock from node x with convert_type
> EX in converting list.
> dlm_empty_lockres() {
>   dlm_pick_migration_target() {
>     pick node 2 as target as its lock is the first one
>     in granted list.
>   }
>   dlm_migrate_lockres() {
>     dlm_mark_lockres_migrating() {
>       res->state |= DLM_LOCK_RES_BLOCK_DIRTY;
>       wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
> 	 //after the above code, we can not dirty lockres any more,
>       // so dlm_thread shuffle list will not run
>                                                                    
downconvert lock from EX to NR
>                                                                    
upconvert lock from NR to EX
> <<< migration may schedule out here, then
> <<< node 2 send down convert request to convert type from EX to
> <<< NR, then send up convert request to convert type from NR to
> <<< EX, at this time, lockres granted list is empty, and two locks
> <<< in the converting list, node x up convert lock followed by
> <<< node 2 up convert lock.
>
> 	 // will set lockres RES_MIGRATING flag, the following
> 	 // lock/unlock can not run
>       dlm_lockres_release_ast(dlm, res);
>     }
>
>     dlm_send_one_lockres()
>                                                                  
dlm_process_recovery_data()
>                                                                     for
(i=0; i<mres->num_locks; i++)
>                                                                       if
(ml->node == dlm->node_num)
>                                                                         for
(j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
>                                                                         
list_for_each_entry(lock, tmpq, list)
>                                                                          if
(lock) break; <<< lock is invalid as grant list is empty.
>                                                                         }
>                                                                         if
(lock->ml.node != ml->node)
>                                                                          
BUG() >>> crash here
>   }
> I see the above locks status from a vmcore of our internal bug.
>
> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
> Cc: Sunil Mushran <sunil.mushran at gmail.com>
> Cc: Srinivas Eeda <srinivas.eeda at oracle.com>
> Cc: <stable at vger.kernel.org>
> ---
>   fs/ocfs2/dlm/dlmrecovery.c |   14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index 7035af0..c2dd258 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1750,13 +1750,13 @@ static int dlm_process_recovery_data(struct
dlm_ctxt *dlm,
>   				     struct dlm_migratable_lockres *mres)
>   {
>   	struct dlm_migratable_lock *ml;
> -	struct list_head *queue;
> +	struct list_head *queue, *iter;
>   	struct list_head *tmpq = NULL;
>   	struct dlm_lock *newlock = NULL;
>   	struct dlm_lockstatus *lksb = NULL;
>   	int ret = 0;
>   	int i, j, bad;
> -	struct dlm_lock *lock = NULL;
> +	struct dlm_lock *lock;
>   	u8 from = O2NM_MAX_NODES;
>   	unsigned int added = 0;
>   	__be64 c;
> @@ -1791,14 +1791,16 @@ static int dlm_process_recovery_data(struct
dlm_ctxt *dlm,
>   			/* MIGRATION ONLY! */
>   			BUG_ON(!(mres->flags & DLM_MRES_MIGRATION));
>   
> +			lock = NULL;
>   			spin_lock(&res->spinlock);
>   			for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
>   				tmpq = dlm_list_idx_to_ptr(res, j);
> -				list_for_each_entry(lock, tmpq, list) {
> -					if (lock->ml.cookie != ml->cookie)
> -						lock = NULL;
> -					else
> +				list_for_each(iter, tmpq) {
> +					lock = list_entry(iter,
> +						  struct dlm_lock, list);
> +					if (lock->ml.cookie == ml->cookie)
>   						break;
> +					lock = NULL;
>   				}
>   				if (lock)
>   					break;