diff options
author | 2017-03-08 23:13:28 -0800 | |
---|---|---|
committer | 2017-03-08 23:36:15 -0800 | |
commit | 52f993b8e89487ec9ee15a7fb4979e0f09a45b27 (patch) | |
tree | d65304486afe0bea4a311c783c0d72791c8c0aa2 /kernel/ipc/sem.c | |
parent | c189ccac5702322ed843fe17057035b7222a59b6 (diff) |
Upgrade to 4.4.50-rt62
The current kernel is based on rt kernel v4.4.6-rt14. We will upgrade it
to 4.4.50-rt62.
The command to achieve it is:
a) Clone a git repo from
git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git
b) Get the diff between this two changesets:
git diff 640eca2901f3435e616157b11379d3223a44b391
705619beeea1b0b48219a683fd1a901a86fdaf5e
where the two commits are:
[yjiang5@jnakajim-build linux-stable-rt]$ git show --oneline --name-only
640eca2901f3435e616157b11379d3223a44b391
640eca2901f3 v4.4.6-rt14
localversion-rt
[yjiang5@jnakajim-build linux-stable-rt]$ git show --oneline --name-only
705619beeea1b0b48219a683fd1a901a86fdaf5e
705619beeea1 Linux 4.4.50-rt62
localversion-rt
c) One patch has been backported thus revert the patch before applying.
filterdiff -p1 -x scripts/package/Makefile
~/tmp/v4.4.6-rt14-4.4.50-rt62.diff |patch -p1 --dry-run
Upstream status: backport
Change-Id: I244d57a32f6066e5a5b9915f9fbf99e7bbca6e01
Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
Diffstat (limited to 'kernel/ipc/sem.c')
-rw-r--r-- | kernel/ipc/sem.c | 142 |
1 files changed, 81 insertions, 61 deletions
diff --git a/kernel/ipc/sem.c b/kernel/ipc/sem.c index dc67f53c0..ef34d7376 100644 --- a/kernel/ipc/sem.c +++ b/kernel/ipc/sem.c @@ -155,14 +155,21 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it); /* * Locking: + * a) global sem_lock() for read/write * sem_undo.id_next, * sem_array.complex_count, - * sem_array.pending{_alter,_cont}, - * sem_array.sem_undo: global sem_lock() for read/write - * sem_undo.proc_next: only "current" is allowed to read/write that field. + * sem_array.complex_mode + * sem_array.pending{_alter,_const}, + * sem_array.sem_undo * + * b) global or semaphore sem_lock() for read/write: * sem_array.sem_base[i].pending_{const,alter}: - * global or semaphore sem_lock() for read/write + * sem_array.complex_mode (for read) + * + * c) special: + * sem_undo_list.list_proc: + * * undo_list->lock for write + * * rcu for read */ #define sc_semmsl sem_ctls[0] @@ -263,24 +270,25 @@ static void sem_rcu_free(struct rcu_head *head) #define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb() /* - * Wait until all currently ongoing simple ops have completed. + * Enter the mode suitable for non-simple operations: * Caller must own sem_perm.lock. - * New simple ops cannot start, because simple ops first check - * that sem_perm.lock is free. - * that a) sem_perm.lock is free and b) complex_count is 0. */ -static void sem_wait_array(struct sem_array *sma) +static void complexmode_enter(struct sem_array *sma) { int i; struct sem *sem; - if (sma->complex_count) { - /* The thread that increased sma->complex_count waited on - * all sem->lock locks. Thus we don't need to wait again. - */ + if (sma->complex_mode) { + /* We are already in complex_mode. Nothing to do */ return; } + /* We need a full barrier after seting complex_mode: + * The write to complex_mode must be visible + * before we read the first sem->lock spinlock state. + */ + smp_store_mb(sma->complex_mode, true); + for (i = 0; i < sma->sem_nsems; i++) { sem = sma->sem_base + i; spin_unlock_wait(&sem->lock); @@ -289,6 +297,28 @@ static void sem_wait_array(struct sem_array *sma) } /* + * Try to leave the mode that disallows simple operations: + * Caller must own sem_perm.lock. + */ +static void complexmode_tryleave(struct sem_array *sma) +{ + if (sma->complex_count) { + /* Complex ops are sleeping. + * We must stay in complex mode + */ + return; + } + /* + * Immediately after setting complex_mode to false, + * a simple op can start. Thus: all memory writes + * performed by the current operation must be visible + * before we set complex_mode to false. + */ + smp_store_release(&sma->complex_mode, false); +} + +#define SEM_GLOBAL_LOCK (-1) +/* * If the request contains only one semaphore operation, and there are * no complex transactions pending, lock only the semaphore involved. * Otherwise, lock the entire semaphore array, since we either have @@ -304,56 +334,42 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, /* Complex operation - acquire a full lock */ ipc_lock_object(&sma->sem_perm); - /* And wait until all simple ops that are processed - * right now have dropped their locks. - */ - sem_wait_array(sma); - return -1; + /* Prevent parallel simple ops */ + complexmode_enter(sma); + return SEM_GLOBAL_LOCK; } /* * Only one semaphore affected - try to optimize locking. - * The rules are: - * - optimized locking is possible if no complex operation - * is either enqueued or processed right now. - * - The test for enqueued complex ops is simple: - * sma->complex_count != 0 - * - Testing for complex ops that are processed right now is - * a bit more difficult. Complex ops acquire the full lock - * and first wait that the running simple ops have completed. - * (see above) - * Thus: If we own a simple lock and the global lock is free - * and complex_count is now 0, then it will stay 0 and - * thus just locking sem->lock is sufficient. + * Optimized locking is possible if no complex operation + * is either enqueued or processed right now. + * + * Both facts are tracked by complex_mode. */ sem = sma->sem_base + sops->sem_num; - if (sma->complex_count == 0) { + /* + * Initial check for complex_mode. Just an optimization, + * no locking, no memory barrier. + */ + if (!sma->complex_mode) { /* * It appears that no complex operation is around. * Acquire the per-semaphore lock. */ spin_lock(&sem->lock); - /* Then check that the global lock is free */ - if (!spin_is_locked(&sma->sem_perm.lock)) { - /* - * We need a memory barrier with acquire semantics, - * otherwise we can race with another thread that does: - * complex_count++; - * spin_unlock(sem_perm.lock); - */ - ipc_smp_acquire__after_spin_is_unlocked(); + /* + * See 51d7d5205d33 + * ("powerpc: Add smp_mb() to arch_spin_is_locked()"): + * A full barrier is required: the write of sem->lock + * must be visible before the read is executed + */ + smp_mb(); - /* - * Now repeat the test of complex_count: - * It can't change anymore until we drop sem->lock. - * Thus: if is now 0, then it will stay 0. - */ - if (sma->complex_count == 0) { - /* fast path successful! */ - return sops->sem_num; - } + if (!smp_load_acquire(&sma->complex_mode)) { + /* fast path successful! */ + return sops->sem_num; } spin_unlock(&sem->lock); } @@ -373,15 +389,16 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, /* Not a false alarm, thus complete the sequence for a * full lock. */ - sem_wait_array(sma); - return -1; + complexmode_enter(sma); + return SEM_GLOBAL_LOCK; } } static inline void sem_unlock(struct sem_array *sma, int locknum) { - if (locknum == -1) { + if (locknum == SEM_GLOBAL_LOCK) { unmerge_queues(sma); + complexmode_tryleave(sma); ipc_unlock_object(&sma->sem_perm); } else { struct sem *sem = sma->sem_base + locknum; @@ -442,7 +459,7 @@ static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns static inline void sem_lock_and_putref(struct sem_array *sma) { sem_lock(sma, NULL, -1); - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); } static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s) @@ -533,6 +550,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params) } sma->complex_count = 0; + sma->complex_mode = true; /* dropped by sem_unlock below */ INIT_LIST_HEAD(&sma->pending_alter); INIT_LIST_HEAD(&sma->pending_const); INIT_LIST_HEAD(&sma->list_id); @@ -1395,7 +1413,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum, rcu_read_unlock(); sem_io = ipc_alloc(sizeof(ushort)*nsems); if (sem_io == NULL) { - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); return -ENOMEM; } @@ -1429,20 +1447,20 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum, if (nsems > SEMMSL_FAST) { sem_io = ipc_alloc(sizeof(ushort)*nsems); if (sem_io == NULL) { - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); return -ENOMEM; } } if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) { - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); err = -EFAULT; goto out_free; } for (i = 0; i < nsems; i++) { if (sem_io[i] > SEMVMX) { - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); err = -ERANGE; goto out_free; } @@ -1732,7 +1750,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid) /* step 2: allocate new undo structure */ new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL); if (!new) { - ipc_rcu_putref(sma, ipc_rcu_free); + ipc_rcu_putref(sma, sem_rcu_free); return ERR_PTR(-ENOMEM); } @@ -2196,10 +2214,10 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it) /* * The proc interface isn't aware of sem_lock(), it calls * ipc_lock_object() directly (in sysvipc_find_ipc). - * In order to stay compatible with sem_lock(), we must wait until - * all simple semop() calls have left their critical regions. + * In order to stay compatible with sem_lock(), we must + * enter / leave complex_mode. */ - sem_wait_array(sma); + complexmode_enter(sma); sem_otime = get_semotime(sma); @@ -2216,6 +2234,8 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it) sem_otime, sma->sem_ctime); + complexmode_tryleave(sma); + return 0; } #endif |