diff options
author | Pierre Peiffer <pierre.peiffer@bull.net> | 2007-10-19 02:40:55 -0400 |
---|---|---|
committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-10-19 14:53:48 -0400 |
commit | c530c6ac7eb1d4ae1ff6b382d9211be446ee82c6 (patch) | |
tree | f36b7323f4c60f859107f74014ae67da6d63d49f /ipc | |
parent | 1b531f213661657d6e1c55cf5c97f649d630c227 (diff) |
IPC: cleanup some code and wrong comments about semundo list managment
Some comments about sem_undo_list seem wrong.
About the comment above unlock_semundo:
"... If task2 now exits before task1 releases the lock (by calling
unlock_semundo()), then task1 will never call spin_unlock(). ..."
This is just wrong, I see no reason for which task1 will not call
spin_unlock... The rest of this comment is also wrong... Unless I
miss something (of course).
Finally, (un)lock_semundo functions are useless, so remove them
for simplification. (this avoids an useless if statement)
Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r-- | ipc/sem.c | 46 |
1 files changed, 6 insertions, 40 deletions
@@ -999,36 +999,6 @@ asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg) | |||
999 | } | 999 | } |
1000 | } | 1000 | } |
1001 | 1001 | ||
1002 | static inline void lock_semundo(void) | ||
1003 | { | ||
1004 | struct sem_undo_list *undo_list; | ||
1005 | |||
1006 | undo_list = current->sysvsem.undo_list; | ||
1007 | if (undo_list) | ||
1008 | spin_lock(&undo_list->lock); | ||
1009 | } | ||
1010 | |||
1011 | /* This code has an interaction with copy_semundo(). | ||
1012 | * Consider; two tasks are sharing the undo_list. task1 | ||
1013 | * acquires the undo_list lock in lock_semundo(). If task2 now | ||
1014 | * exits before task1 releases the lock (by calling | ||
1015 | * unlock_semundo()), then task1 will never call spin_unlock(). | ||
1016 | * This leave the sem_undo_list in a locked state. If task1 now creats task3 | ||
1017 | * and once again shares the sem_undo_list, the sem_undo_list will still be | ||
1018 | * locked, and future SEM_UNDO operations will deadlock. This case is | ||
1019 | * dealt with in copy_semundo() by having it reinitialize the spin lock when | ||
1020 | * the refcnt goes from 1 to 2. | ||
1021 | */ | ||
1022 | static inline void unlock_semundo(void) | ||
1023 | { | ||
1024 | struct sem_undo_list *undo_list; | ||
1025 | |||
1026 | undo_list = current->sysvsem.undo_list; | ||
1027 | if (undo_list) | ||
1028 | spin_unlock(&undo_list->lock); | ||
1029 | } | ||
1030 | |||
1031 | |||
1032 | /* If the task doesn't already have a undo_list, then allocate one | 1002 | /* If the task doesn't already have a undo_list, then allocate one |
1033 | * here. We guarantee there is only one thread using this undo list, | 1003 | * here. We guarantee there is only one thread using this undo list, |
1034 | * and current is THE ONE | 1004 | * and current is THE ONE |
@@ -1089,9 +1059,9 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid) | |||
1089 | if (error) | 1059 | if (error) |
1090 | return ERR_PTR(error); | 1060 | return ERR_PTR(error); |
1091 | 1061 | ||
1092 | lock_semundo(); | 1062 | spin_lock(&ulp->lock); |
1093 | un = lookup_undo(ulp, semid); | 1063 | un = lookup_undo(ulp, semid); |
1094 | unlock_semundo(); | 1064 | spin_unlock(&ulp->lock); |
1095 | if (likely(un!=NULL)) | 1065 | if (likely(un!=NULL)) |
1096 | goto out; | 1066 | goto out; |
1097 | 1067 | ||
@@ -1114,10 +1084,10 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid) | |||
1114 | new->semadj = (short *) &new[1]; | 1084 | new->semadj = (short *) &new[1]; |
1115 | new->semid = semid; | 1085 | new->semid = semid; |
1116 | 1086 | ||
1117 | lock_semundo(); | 1087 | spin_lock(&ulp->lock); |
1118 | un = lookup_undo(ulp, semid); | 1088 | un = lookup_undo(ulp, semid); |
1119 | if (un) { | 1089 | if (un) { |
1120 | unlock_semundo(); | 1090 | spin_unlock(&ulp->lock); |
1121 | kfree(new); | 1091 | kfree(new); |
1122 | ipc_lock_by_ptr(&sma->sem_perm); | 1092 | ipc_lock_by_ptr(&sma->sem_perm); |
1123 | ipc_rcu_putref(sma); | 1093 | ipc_rcu_putref(sma); |
@@ -1128,7 +1098,7 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid) | |||
1128 | ipc_rcu_putref(sma); | 1098 | ipc_rcu_putref(sma); |
1129 | if (sma->sem_perm.deleted) { | 1099 | if (sma->sem_perm.deleted) { |
1130 | sem_unlock(sma); | 1100 | sem_unlock(sma); |
1131 | unlock_semundo(); | 1101 | spin_unlock(&ulp->lock); |
1132 | kfree(new); | 1102 | kfree(new); |
1133 | un = ERR_PTR(-EIDRM); | 1103 | un = ERR_PTR(-EIDRM); |
1134 | goto out; | 1104 | goto out; |
@@ -1139,7 +1109,7 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid) | |||
1139 | sma->undo = new; | 1109 | sma->undo = new; |
1140 | sem_unlock(sma); | 1110 | sem_unlock(sma); |
1141 | un = new; | 1111 | un = new; |
1142 | unlock_semundo(); | 1112 | spin_unlock(&ulp->lock); |
1143 | out: | 1113 | out: |
1144 | return un; | 1114 | return un; |
1145 | } | 1115 | } |
@@ -1315,10 +1285,6 @@ asmlinkage long sys_semop (int semid, struct sembuf __user *tsops, unsigned nsop | |||
1315 | 1285 | ||
1316 | /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between | 1286 | /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between |
1317 | * parent and child tasks. | 1287 | * parent and child tasks. |
1318 | * | ||
1319 | * See the notes above unlock_semundo() regarding the spin_lock_init() | ||
1320 | * in this code. Initialize the undo_list->lock here instead of get_undo_list() | ||
1321 | * because of the reasoning in the comment above unlock_semundo. | ||
1322 | */ | 1288 | */ |
1323 | 1289 | ||
1324 | int copy_semundo(unsigned long clone_flags, struct task_struct *tsk) | 1290 | int copy_semundo(unsigned long clone_flags, struct task_struct *tsk) |