cpumask_t cpus_allowed; /* CPUs allowed to tasks in cpuset */
nodemask_t mems_allowed; /* Memory Nodes allowed to tasks */
+ /*
+ * Count is atomic so can incr (fork) or decr (exit) without a lock.
+ */
atomic_t count; /* count tasks using this cpuset */
/*
static struct super_block *cpuset_sb = NULL;
/*
- * cpuset_sem should be held by anyone who is depending on the children
- * or sibling lists of any cpuset, or performing non-atomic operations
- * on the flags or *_allowed values of a cpuset, such as raising the
- * CS_REMOVED flag bit iff it is not already raised, or reading and
- * conditionally modifying the *_allowed values. One kernel global
- * cpuset semaphore should be sufficient - these things don't change
- * that much.
- *
- * The code that modifies cpusets holds cpuset_sem across the entire
- * operation, from cpuset_common_file_write() down, single threading
- * all cpuset modifications (except for counter manipulations from
- * fork and exit) across the system. This presumes that cpuset
- * modifications are rare - better kept simple and safe, even if slow.
- *
- * The code that reads cpusets, such as in cpuset_common_file_read()
- * and below, only holds cpuset_sem across small pieces of code, such
- * as when reading out possibly multi-word cpumasks and nodemasks, as
- * the risks are less, and the desire for performance a little greater.
- * The proc_cpuset_show() routine needs to hold cpuset_sem to insure
- * that no cs->dentry is NULL, as it walks up the cpuset tree to root.
- *
- * The hooks from fork and exit, cpuset_fork() and cpuset_exit(), don't
- * (usually) grab cpuset_sem. These are the two most performance
- * critical pieces of code here. The exception occurs on exit(),
- * when a task in a notify_on_release cpuset exits. Then cpuset_sem
+ * We have two global cpuset semaphores below. They can nest.
+ * It is ok to first take manage_sem, then nest callback_sem. We also
+ * require taking task_lock() when dereferencing a tasks cpuset pointer.
+ * See "The task_lock() exception", at the end of this comment.
+ *
+ * A task must hold both semaphores to modify cpusets. If a task
+ * holds manage_sem, then it blocks others wanting that semaphore,
+ * ensuring that it is the only task able to also acquire callback_sem
+ * and be able to modify cpusets. It can perform various checks on
+ * the cpuset structure first, knowing nothing will change. It can
+ * also allocate memory while just holding manage_sem. While it is
+ * performing these checks, various callback routines can briefly
+ * acquire callback_sem to query cpusets. Once it is ready to make
+ * the changes, it takes callback_sem, blocking everyone else.
+ *
+ * Calls to the kernel memory allocator can not be made while holding
+ * callback_sem, as that would risk double tripping on callback_sem
+ * from one of the callbacks into the cpuset code from within
+ * __alloc_pages().
+ *
+ * If a task is only holding callback_sem, then it has read-only
+ * access to cpusets.
+ *
+ * The task_struct fields mems_allowed and mems_generation may only
+ * be accessed in the context of that task, so require no locks.
+ *
+ * Any task can increment and decrement the count field without lock.
+ * So in general, code holding manage_sem or callback_sem can't rely
+ * on the count field not changing. However, if the count goes to
+ * zero, then only attach_task(), which holds both semaphores, can
+ * increment it again. Because a count of zero means that no tasks
+ * are currently attached, therefore there is no way a task attached
+ * to that cpuset can fork (the other way to increment the count).
+ * So code holding manage_sem or callback_sem can safely assume that
+ * if the count is zero, it will stay zero. Similarly, if a task
+ * holds manage_sem or callback_sem on a cpuset with zero count, it
+ * knows that the cpuset won't be removed, as cpuset_rmdir() needs
+ * both of those semaphores.
+ *
+ * A possible optimization to improve parallelism would be to make
+ * callback_sem a R/W semaphore (rwsem), allowing the callback routines
+ * to proceed in parallel, with read access, until the holder of
+ * manage_sem needed to take this rwsem for exclusive write access
+ * and modify some cpusets.
+ *
+ * The cpuset_common_file_write handler for operations that modify
+ * the cpuset hierarchy holds manage_sem across the entire operation,
+ * single threading all such cpuset modifications across the system.
+ *
+ * The cpuset_common_file_read() handlers only hold callback_sem across
+ * small pieces of code, such as when reading out possibly multi-word
+ * cpumasks and nodemasks.
+ *
+ * The fork and exit callbacks cpuset_fork() and cpuset_exit(), don't
+ * (usually) take either semaphore. These are the two most performance
+ * critical pieces of code here. The exception occurs on cpuset_exit(),
+ * when a task in a notify_on_release cpuset exits. Then manage_sem
* is taken, and if the cpuset count is zero, a usermode call made
* to /sbin/cpuset_release_agent with the name of the cpuset (path
* relative to the root of cpuset file system) as the argument.
*
- * A cpuset can only be deleted if both its 'count' of using tasks is
- * zero, and its list of 'children' cpusets is empty. Since all tasks
- * in the system use _some_ cpuset, and since there is always at least
- * one task in the system (init, pid == 1), therefore, top_cpuset
- * always has either children cpusets and/or using tasks. So no need
- * for any special hack to ensure that top_cpuset cannot be deleted.
+ * A cpuset can only be deleted if both its 'count' of using tasks
+ * is zero, and its list of 'children' cpusets is empty. Since all
+ * tasks in the system use _some_ cpuset, and since there is always at
+ * least one task in the system (init, pid == 1), therefore, top_cpuset
+ * always has either children cpusets and/or using tasks. So we don't
+ * need a special hack to ensure that top_cpuset cannot be deleted.
+ *
+ * The above "Tale of Two Semaphores" would be complete, but for:
+ *
+ * The task_lock() exception
+ *
+ * The need for this exception arises from the action of attach_task(),
+ * which overwrites one tasks cpuset pointer with another. It does
+ * so using both semaphores, however there are several performance
+ * critical places that need to reference task->cpuset without the
+ * expense of grabbing a system global semaphore. Therefore except as
+ * noted below, when dereferencing or, as in attach_task(), modifying
+ * a tasks cpuset pointer we use task_lock(), which acts on a spinlock
+ * (task->alloc_lock) already in the task_struct routinely used for
+ * such matters.
*/
-static DECLARE_MUTEX(cpuset_sem);
+static DECLARE_MUTEX(manage_sem);
+static DECLARE_MUTEX(callback_sem);
/*
* A couple of forward declarations required, due to cyclic reference loop:
}
/*
- * Call with cpuset_sem held. Writes path of cpuset into buf.
+ * Call with manage_sem held. Writes path of cpuset into buf.
* Returns 0 on success, -errno on error.
*/
* status of the /sbin/cpuset_release_agent task, so no sense holding
* our caller up for that.
*
- * The simple act of forking that task might require more memory,
- * which might need cpuset_sem. So this routine must be called while
- * cpuset_sem is not held, to avoid a possible deadlock. See also
- * comments for check_for_release(), below.
+ * When we had only one cpuset semaphore, we had to call this
+ * without holding it, to avoid deadlock when call_usermodehelper()
+ * allocated memory. With two locks, we could now call this while
+ * holding manage_sem, but we still don't, so as to minimize
+ * the time manage_sem is held.
*/
static void cpuset_release_agent(const char *pathbuf)
* cs is notify_on_release() and now both the user count is zero and
* the list of children is empty, prepare cpuset path in a kmalloc'd
* buffer, to be returned via ppathbuf, so that the caller can invoke
- * cpuset_release_agent() with it later on, once cpuset_sem is dropped.
- * Call here with cpuset_sem held.
+ * cpuset_release_agent() with it later on, once manage_sem is dropped.
+ * Call here with manage_sem held.
*
* This check_for_release() routine is responsible for kmalloc'ing
* pathbuf. The above cpuset_release_agent() is responsible for
* kfree'ing pathbuf. The caller of these routines is responsible
* for providing a pathbuf pointer, initialized to NULL, then
- * calling check_for_release() with cpuset_sem held and the address
- * of the pathbuf pointer, then dropping cpuset_sem, then calling
+ * calling check_for_release() with manage_sem held and the address
+ * of the pathbuf pointer, then dropping manage_sem, then calling
* cpuset_release_agent() with pathbuf, as set by check_for_release().
*/
* One way or another, we guarantee to return some non-empty subset
* of cpu_online_map.
*
- * Call with cpuset_sem held.
+ * Call with callback_sem held.
*/
static void guarantee_online_cpus(const struct cpuset *cs, cpumask_t *pmask)
* One way or another, we guarantee to return some non-empty subset
* of node_online_map.
*
- * Call with cpuset_sem held.
+ * Call with callback_sem held.
*/
static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
}
/*
- * Refresh current tasks mems_allowed and mems_generation from
- * current tasks cpuset. Call with cpuset_sem held.
- *
- * Be sure to call refresh_mems() on any cpuset operation which
- * (1) holds cpuset_sem, and (2) might possibly alloc memory.
- * Call after obtaining cpuset_sem lock, before any possible
- * allocation. Otherwise one risks trying to allocate memory
- * while the task cpuset_mems_generation is not the same as
- * the mems_generation in its cpuset, which would deadlock on
- * cpuset_sem in cpuset_update_current_mems_allowed().
- *
- * Since we hold cpuset_sem, once refresh_mems() is called, the
- * test (current->cpuset_mems_generation != cs->mems_generation)
- * in cpuset_update_current_mems_allowed() will remain false,
- * until we drop cpuset_sem. Anyone else who would change our
- * cpusets mems_generation needs to lock cpuset_sem first.
+ * Refresh current tasks mems_allowed and mems_generation from current
+ * tasks cpuset.
+ *
+ * Call without callback_sem or task_lock() held. May be called with
+ * or without manage_sem held. Will acquire task_lock() and might
+ * acquire callback_sem during call.
+ *
+ * The task_lock() is required to dereference current->cpuset safely.
+ * Without it, we could pick up the pointer value of current->cpuset
+ * in one instruction, and then attach_task could give us a different
+ * cpuset, and then the cpuset we had could be removed and freed,
+ * and then on our next instruction, we could dereference a no longer
+ * valid cpuset pointer to get its mems_generation field.
+ *
+ * This routine is needed to update the per-task mems_allowed data,
+ * within the tasks context, when it is trying to allocate memory
+ * (in various mm/mempolicy.c routines) and notices that some other
+ * task has been modifying its cpuset.
*/
static void refresh_mems(void)
{
- struct cpuset *cs = current->cpuset;
+ int my_cpusets_mem_gen;
+
+ task_lock(current);
+ my_cpusets_mem_gen = current->cpuset->mems_generation;
+ task_unlock(current);
- if (current->cpuset_mems_generation != cs->mems_generation) {
+ if (current->cpuset_mems_generation != my_cpusets_mem_gen) {
+ struct cpuset *cs;
+
+ down(&callback_sem);
+ task_lock(current);
+ cs = current->cpuset;
guarantee_online_mems(cs, ¤t->mems_allowed);
current->cpuset_mems_generation = cs->mems_generation;
+ task_unlock(current);
+ up(&callback_sem);
}
}
*
* One cpuset is a subset of another if all its allowed CPUs and
* Memory Nodes are a subset of the other, and its exclusive flags
- * are only set if the other's are set.
+ * are only set if the other's are set. Call holding manage_sem.
*/
static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
* If we replaced the flag and mask values of the current cpuset
* (cur) with those values in the trial cpuset (trial), would
* our various subset and exclusive rules still be valid? Presumes
- * cpuset_sem held.
+ * manage_sem held.
*
* 'cur' is the address of an actual, in-use cpuset. Operations
* such as list traversal that depend on the actual address of the
* exclusive child cpusets
* Build these two partitions by calling partition_sched_domains
*
- * Call with cpuset_sem held. May nest a call to the
+ * Call with manage_sem held. May nest a call to the
* lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
*/
unlock_cpu_hotplug();
}
+/*
+ * Call with manage_sem held. May take callback_sem during call.
+ */
+
static int update_cpumask(struct cpuset *cs, char *buf)
{
struct cpuset trialcs;
if (retval < 0)
return retval;
cpus_unchanged = cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
+ down(&callback_sem);
cs->cpus_allowed = trialcs.cpus_allowed;
+ up(&callback_sem);
if (is_cpu_exclusive(cs) && !cpus_unchanged)
update_cpu_domains(cs);
return 0;
}
+/*
+ * Call with manage_sem held. May take callback_sem during call.
+ */
+
static int update_nodemask(struct cpuset *cs, char *buf)
{
struct cpuset trialcs;
return -ENOSPC;
retval = validate_change(cs, &trialcs);
if (retval == 0) {
+ down(&callback_sem);
cs->mems_allowed = trialcs.mems_allowed;
atomic_inc(&cpuset_mems_generation);
cs->mems_generation = atomic_read(&cpuset_mems_generation);
+ up(&callback_sem);
}
return retval;
}
* CS_NOTIFY_ON_RELEASE)
* cs: the cpuset to update
* buf: the buffer where we read the 0 or 1
+ *
+ * Call with manage_sem held.
*/
static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
return err;
cpu_exclusive_changed =
(is_cpu_exclusive(cs) != is_cpu_exclusive(&trialcs));
+ down(&callback_sem);
if (turning_on)
set_bit(bit, &cs->flags);
else
clear_bit(bit, &cs->flags);
+ up(&callback_sem);
if (cpu_exclusive_changed)
update_cpu_domains(cs);
return 0;
}
+/*
+ * Attack task specified by pid in 'pidbuf' to cpuset 'cs', possibly
+ * writing the path of the old cpuset in 'ppathbuf' if it needs to be
+ * notified on release.
+ *
+ * Call holding manage_sem. May take callback_sem and task_lock of
+ * the task 'pid' during call.
+ */
+
static int attach_task(struct cpuset *cs, char *pidbuf, char **ppathbuf)
{
pid_t pid;
read_lock(&tasklist_lock);
tsk = find_task_by_pid(pid);
- if (!tsk) {
+ if (!tsk || tsk->flags & PF_EXITING) {
read_unlock(&tasklist_lock);
return -ESRCH;
}
get_task_struct(tsk);
}
+ down(&callback_sem);
+
task_lock(tsk);
oldcs = tsk->cpuset;
if (!oldcs) {
task_unlock(tsk);
+ up(&callback_sem);
put_task_struct(tsk);
return -ESRCH;
}
guarantee_online_cpus(cs, &cpus);
set_cpus_allowed(tsk, cpus);
+ up(&callback_sem);
put_task_struct(tsk);
if (atomic_dec_and_test(&oldcs->count))
check_for_release(oldcs, ppathbuf);
}
buffer[nbytes] = 0; /* nul-terminate */
- down(&cpuset_sem);
+ down(&manage_sem);
if (is_removed(cs)) {
retval = -ENODEV;
if (retval == 0)
retval = nbytes;
out2:
- up(&cpuset_sem);
+ up(&manage_sem);
cpuset_release_agent(pathbuf);
out1:
kfree(buffer);
{
cpumask_t mask;
- down(&cpuset_sem);
+ down(&callback_sem);
mask = cs->cpus_allowed;
- up(&cpuset_sem);
+ up(&callback_sem);
return cpulist_scnprintf(page, PAGE_SIZE, mask);
}
{
nodemask_t mask;
- down(&cpuset_sem);
+ down(&callback_sem);
mask = cs->mems_allowed;
- up(&cpuset_sem);
+ up(&callback_sem);
return nodelist_scnprintf(page, PAGE_SIZE, mask);
}
/*
* Load into 'pidarray' up to 'npids' of the tasks using cpuset 'cs'.
- * Return actual number of pids loaded.
+ * Return actual number of pids loaded. No need to task_lock(p)
+ * when reading out p->cpuset, as we don't really care if it changes
+ * on the next cycle, and we are not going to try to dereference it.
*/
static inline int pid_array_load(pid_t *pidarray, int npids, struct cpuset *cs)
{
return cnt;
}
+/*
+ * Handle an open on 'tasks' file. Prepare a buffer listing the
+ * process id's of tasks currently attached to the cpuset being opened.
+ *
+ * Does not require any specific cpuset semaphores, and does not take any.
+ */
static int cpuset_tasks_open(struct inode *unused, struct file *file)
{
struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
if (!cs)
return -ENOMEM;
- down(&cpuset_sem);
+ down(&manage_sem);
refresh_mems();
cs->flags = 0;
if (notify_on_release(parent))
cs->parent = parent;
+ down(&callback_sem);
list_add(&cs->sibling, &cs->parent->children);
+ up(&callback_sem);
err = cpuset_create_dir(cs, name, mode);
if (err < 0)
goto err;
/*
- * Release cpuset_sem before cpuset_populate_dir() because it
+ * Release manage_sem before cpuset_populate_dir() because it
* will down() this new directory's i_sem and if we race with
* another mkdir, we might deadlock.
*/
- up(&cpuset_sem);
+ up(&manage_sem);
err = cpuset_populate_dir(cs->dentry);
/* If err < 0, we have a half-filled directory - oh well ;) */
return 0;
err:
list_del(&cs->sibling);
- up(&cpuset_sem);
+ up(&manage_sem);
kfree(cs);
return err;
}
/* the vfs holds both inode->i_sem already */
- down(&cpuset_sem);
+ down(&manage_sem);
refresh_mems();
if (atomic_read(&cs->count) > 0) {
- up(&cpuset_sem);
+ up(&manage_sem);
return -EBUSY;
}
if (!list_empty(&cs->children)) {
- up(&cpuset_sem);
+ up(&manage_sem);
return -EBUSY;
}
parent = cs->parent;
+ down(&callback_sem);
set_bit(CS_REMOVED, &cs->flags);
if (is_cpu_exclusive(cs))
update_cpu_domains(cs);
list_del(&cs->sibling); /* delete my sibling from parent->children */
- if (list_empty(&parent->children))
- check_for_release(parent, &pathbuf);
spin_lock(&cs->dentry->d_lock);
d = dget(cs->dentry);
cs->dentry = NULL;
spin_unlock(&d->d_lock);
cpuset_d_remove_dir(d);
dput(d);
- up(&cpuset_sem);
+ up(&callback_sem);
+ if (list_empty(&parent->children))
+ check_for_release(parent, &pathbuf);
+ up(&manage_sem);
cpuset_release_agent(pathbuf);
return 0;
}
* cpuset_fork - attach newly forked task to its parents cpuset.
* @tsk: pointer to task_struct of forking parent process.
*
- * Description: By default, on fork, a task inherits its
- * parent's cpuset. The pointer to the shared cpuset is
- * automatically copied in fork.c by dup_task_struct().
- * This cpuset_fork() routine need only increment the usage
- * counter in that cpuset.
+ * Description: A task inherits its parent's cpuset at fork().
+ *
+ * A pointer to the shared cpuset was automatically copied in fork.c
+ * by dup_task_struct(). However, we ignore that copy, since it was
+ * not made under the protection of task_lock(), so might no longer be
+ * a valid cpuset pointer. attach_task() might have already changed
+ * current->cpuset, allowing the previously referenced cpuset to
+ * be removed and freed. Instead, we task_lock(current) and copy
+ * its present value of current->cpuset for our freshly forked child.
+ *
+ * At the point that cpuset_fork() is called, 'current' is the parent
+ * task, and the passed argument 'child' points to the child task.
**/
-void cpuset_fork(struct task_struct *tsk)
+void cpuset_fork(struct task_struct *child)
{
- atomic_inc(&tsk->cpuset->count);
+ task_lock(current);
+ child->cpuset = current->cpuset;
+ atomic_inc(&child->cpuset->count);
+ task_unlock(current);
}
/**
*
* Description: Detach cpuset from @tsk and release it.
*
- * Note that cpusets marked notify_on_release force every task
- * in them to take the global cpuset_sem semaphore when exiting.
- * This could impact scaling on very large systems. Be reluctant
- * to use notify_on_release cpusets where very high task exit
- * scaling is required on large systems.
- *
- * Don't even think about derefencing 'cs' after the cpuset use
- * count goes to zero, except inside a critical section guarded
- * by the cpuset_sem semaphore. If you don't hold cpuset_sem,
- * then a zero cpuset use count is a license to any other task to
- * nuke the cpuset immediately.
+ * Note that cpusets marked notify_on_release force every task in
+ * them to take the global manage_sem semaphore when exiting.
+ * This could impact scaling on very large systems. Be reluctant to
+ * use notify_on_release cpusets where very high task exit scaling
+ * is required on large systems.
+ *
+ * Don't even think about derefencing 'cs' after the cpuset use count
+ * goes to zero, except inside a critical section guarded by manage_sem
+ * or callback_sem. Otherwise a zero cpuset use count is a license to
+ * any other task to nuke the cpuset immediately, via cpuset_rmdir().
+ *
+ * This routine has to take manage_sem, not callback_sem, because
+ * it is holding that semaphore while calling check_for_release(),
+ * which calls kmalloc(), so can't be called holding callback__sem().
+ *
+ * We don't need to task_lock() this reference to tsk->cpuset,
+ * because tsk is already marked PF_EXITING, so attach_task() won't
+ * mess with it.
**/
void cpuset_exit(struct task_struct *tsk)
{
struct cpuset *cs;
- task_lock(tsk);
+ BUG_ON(!(tsk->flags & PF_EXITING));
+
cs = tsk->cpuset;
tsk->cpuset = NULL;
- task_unlock(tsk);
if (notify_on_release(cs)) {
char *pathbuf = NULL;
- down(&cpuset_sem);
+ down(&manage_sem);
if (atomic_dec_and_test(&cs->count))
check_for_release(cs, &pathbuf);
- up(&cpuset_sem);
+ up(&manage_sem);
cpuset_release_agent(pathbuf);
} else {
atomic_dec(&cs->count);
{
cpumask_t mask;
- down(&cpuset_sem);
+ down(&callback_sem);
task_lock((struct task_struct *)tsk);
guarantee_online_cpus(tsk->cpuset, &mask);
task_unlock((struct task_struct *)tsk);
- up(&cpuset_sem);
+ up(&callback_sem);
return mask;
}
* If the current tasks cpusets mems_allowed changed behind our backs,
* update current->mems_allowed and mems_generation to the new value.
* Do not call this routine if in_interrupt().
+ *
+ * Call without callback_sem or task_lock() held. May be called
+ * with or without manage_sem held. Unless exiting, it will acquire
+ * task_lock(). Also might acquire callback_sem during call to
+ * refresh_mems().
*/
void cpuset_update_current_mems_allowed(void)
{
- struct cpuset *cs = current->cpuset;
+ struct cpuset *cs;
+ int need_to_refresh = 0;
+ task_lock(current);
+ cs = current->cpuset;
if (!cs)
- return; /* task is exiting */
- if (current->cpuset_mems_generation != cs->mems_generation) {
- down(&cpuset_sem);
+ goto done;
+ if (current->cpuset_mems_generation != cs->mems_generation)
+ need_to_refresh = 1;
+done:
+ task_unlock(current);
+ if (need_to_refresh)
refresh_mems();
- up(&cpuset_sem);
- }
}
/**
/*
* nearest_exclusive_ancestor() - Returns the nearest mem_exclusive
- * ancestor to the specified cpuset. Call while holding cpuset_sem.
+ * ancestor to the specified cpuset. Call holding callback_sem.
* If no ancestor is mem_exclusive (an unusual configuration), then
* returns the root cpuset.
*/
* GFP_KERNEL allocations are not so marked, so can escape to the
* nearest mem_exclusive ancestor cpuset.
*
- * Scanning up parent cpusets requires cpuset_sem. The __alloc_pages()
+ * Scanning up parent cpusets requires callback_sem. The __alloc_pages()
* routine only calls here with __GFP_HARDWALL bit _not_ set if
* it's a GFP_KERNEL allocation, and all nodes in the current tasks
* mems_allowed came up empty on the first pass over the zonelist.
* So only GFP_KERNEL allocations, if all nodes in the cpuset are
- * short of memory, might require taking the cpuset_sem semaphore.
+ * short of memory, might require taking the callback_sem semaphore.
*
* The first loop over the zonelist in mm/page_alloc.c:__alloc_pages()
* calls here with __GFP_HARDWALL always set in gfp_mask, enforcing
return 0;
/* Not hardwall and node outside mems_allowed: scan up cpusets */
- down(&cpuset_sem);
- cs = current->cpuset;
- if (!cs)
- goto done; /* current task exiting */
- cs = nearest_exclusive_ancestor(cs);
+ down(&callback_sem);
+
+ if (current->flags & PF_EXITING) /* Let dying task have memory */
+ return 1;
+ task_lock(current);
+ cs = nearest_exclusive_ancestor(current->cpuset);
+ task_unlock(current);
+
allowed = node_isset(node, cs->mems_allowed);
-done:
- up(&cpuset_sem);
+ up(&callback_sem);
return allowed;
}
* determine if task @p's memory usage might impact the memory
* available to the current task.
*
- * Acquires cpuset_sem - not suitable for calling from a fast path.
+ * Acquires callback_sem - not suitable for calling from a fast path.
**/
int cpuset_excl_nodes_overlap(const struct task_struct *p)
const struct cpuset *cs1, *cs2; /* my and p's cpuset ancestors */
int overlap = 0; /* do cpusets overlap? */
- down(&cpuset_sem);
- cs1 = current->cpuset;
- if (!cs1)
- goto done; /* current task exiting */
- cs2 = p->cpuset;
- if (!cs2)
- goto done; /* task p is exiting */
- cs1 = nearest_exclusive_ancestor(cs1);
- cs2 = nearest_exclusive_ancestor(cs2);
+ down(&callback_sem);
+
+ task_lock(current);
+ if (current->flags & PF_EXITING) {
+ task_unlock(current);
+ goto done;
+ }
+ cs1 = nearest_exclusive_ancestor(current->cpuset);
+ task_unlock(current);
+
+ task_lock((struct task_struct *)p);
+ if (p->flags & PF_EXITING) {
+ task_unlock((struct task_struct *)p);
+ goto done;
+ }
+ cs2 = nearest_exclusive_ancestor(p->cpuset);
+ task_unlock((struct task_struct *)p);
+
overlap = nodes_intersects(cs1->mems_allowed, cs2->mems_allowed);
done:
- up(&cpuset_sem);
+ up(&callback_sem);
return overlap;
}
* proc_cpuset_show()
* - Print tasks cpuset path into seq_file.
* - Used for /proc/<pid>/cpuset.
+ * - No need to task_lock(tsk) on this tsk->cpuset reference, as it
+ * doesn't really matter if tsk->cpuset changes after we read it,
+ * and we take manage_sem, keeping attach_task() from changing it
+ * anyway.
*/
static int proc_cpuset_show(struct seq_file *m, void *v)
return -ENOMEM;
tsk = m->private;
- down(&cpuset_sem);
- task_lock(tsk);
+ down(&manage_sem);
cs = tsk->cpuset;
- task_unlock(tsk);
if (!cs) {
retval = -EINVAL;
goto out;
seq_puts(m, buf);
seq_putc(m, '\n');
out:
- up(&cpuset_sem);
+ up(&manage_sem);
kfree(buf);
return retval;
}
projects / linux-2.6 / commitdiff