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-rw-r--r--kernel/cpuset.c109
1 files changed, 69 insertions, 40 deletions
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1f06e7690106..79866bc6b3a1 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -180,6 +180,42 @@ static struct super_block *cpuset_sb = NULL;
*/
static DECLARE_MUTEX(cpuset_sem);
+static struct task_struct *cpuset_sem_owner;
+static int cpuset_sem_depth;
+
+/*
+ * The global cpuset semaphore cpuset_sem can be needed by the
+ * memory allocator to update a tasks mems_allowed (see the calls
+ * to cpuset_update_current_mems_allowed()) or to walk up the
+ * cpuset hierarchy to find a mem_exclusive cpuset see the calls
+ * to cpuset_excl_nodes_overlap()).
+ *
+ * But if the memory allocation is being done by cpuset.c code, it
+ * usually already holds cpuset_sem. Double tripping on a kernel
+ * semaphore deadlocks the current task, and any other task that
+ * subsequently tries to obtain the lock.
+ *
+ * Run all up's and down's on cpuset_sem through the following
+ * wrappers, which will detect this nested locking, and avoid
+ * deadlocking.
+ */
+
+static inline void cpuset_down(struct semaphore *psem)
+{
+ if (cpuset_sem_owner != current) {
+ down(psem);
+ cpuset_sem_owner = current;
+ }
+ cpuset_sem_depth++;
+}
+
+static inline void cpuset_up(struct semaphore *psem)
+{
+ if (--cpuset_sem_depth == 0) {
+ cpuset_sem_owner = NULL;
+ up(psem);
+ }
+}
/*
* A couple of forward declarations required, due to cyclic reference loop:
@@ -522,19 +558,10 @@ 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.
+ * 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)
@@ -840,7 +867,7 @@ static ssize_t cpuset_common_file_write(struct file *file, const char __user *us
}
buffer[nbytes] = 0; /* nul-terminate */
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
if (is_removed(cs)) {
retval = -ENODEV;
@@ -874,7 +901,7 @@ static ssize_t cpuset_common_file_write(struct file *file, const char __user *us
if (retval == 0)
retval = nbytes;
out2:
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
cpuset_release_agent(pathbuf);
out1:
kfree(buffer);
@@ -914,9 +941,9 @@ static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
{
cpumask_t mask;
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
mask = cs->cpus_allowed;
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return cpulist_scnprintf(page, PAGE_SIZE, mask);
}
@@ -925,9 +952,9 @@ static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
{
nodemask_t mask;
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
mask = cs->mems_allowed;
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return nodelist_scnprintf(page, PAGE_SIZE, mask);
}
@@ -972,6 +999,10 @@ static ssize_t cpuset_common_file_read(struct file *file, char __user *buf,
*s++ = '\n';
*s = '\0';
+ /* Do nothing if *ppos is at the eof or beyond the eof. */
+ if (s - page <= *ppos)
+ return 0;
+
start = page + *ppos;
n = s - start;
retval = n - copy_to_user(buf, start, min(n, nbytes));
@@ -1330,8 +1361,7 @@ static long cpuset_create(struct cpuset *parent, const char *name, int mode)
if (!cs)
return -ENOMEM;
- down(&cpuset_sem);
- refresh_mems();
+ cpuset_down(&cpuset_sem);
cs->flags = 0;
if (notify_on_release(parent))
set_bit(CS_NOTIFY_ON_RELEASE, &cs->flags);
@@ -1356,14 +1386,14 @@ static long cpuset_create(struct cpuset *parent, const char *name, int mode)
* will down() this new directory's i_sem and if we race with
* another mkdir, we might deadlock.
*/
- up(&cpuset_sem);
+ cpuset_up(&cpuset_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);
+ cpuset_up(&cpuset_sem);
kfree(cs);
return err;
}
@@ -1385,14 +1415,13 @@ static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
/* the vfs holds both inode->i_sem already */
- down(&cpuset_sem);
- refresh_mems();
+ cpuset_down(&cpuset_sem);
if (atomic_read(&cs->count) > 0) {
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return -EBUSY;
}
if (!list_empty(&cs->children)) {
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return -EBUSY;
}
parent = cs->parent;
@@ -1408,7 +1437,7 @@ static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
spin_unlock(&d->d_lock);
cpuset_d_remove_dir(d);
dput(d);
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
cpuset_release_agent(pathbuf);
return 0;
}
@@ -1511,10 +1540,10 @@ void cpuset_exit(struct task_struct *tsk)
if (notify_on_release(cs)) {
char *pathbuf = NULL;
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
if (atomic_dec_and_test(&cs->count))
check_for_release(cs, &pathbuf);
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
cpuset_release_agent(pathbuf);
} else {
atomic_dec(&cs->count);
@@ -1535,11 +1564,11 @@ cpumask_t cpuset_cpus_allowed(const struct task_struct *tsk)
{
cpumask_t mask;
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
task_lock((struct task_struct *)tsk);
guarantee_online_cpus(tsk->cpuset, &mask);
task_unlock((struct task_struct *)tsk);
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return mask;
}
@@ -1564,9 +1593,9 @@ void cpuset_update_current_mems_allowed(void)
if (!cs)
return; /* task is exiting */
if (current->cpuset_mems_generation != cs->mems_generation) {
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
refresh_mems();
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
}
}
@@ -1665,14 +1694,14 @@ int cpuset_zone_allowed(struct zone *z, unsigned int __nocast gfp_mask)
return 0;
/* Not hardwall and node outside mems_allowed: scan up cpusets */
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
cs = current->cpuset;
if (!cs)
goto done; /* current task exiting */
cs = nearest_exclusive_ancestor(cs);
allowed = node_isset(node, cs->mems_allowed);
done:
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return allowed;
}
@@ -1693,7 +1722,7 @@ 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);
+ cpuset_down(&cpuset_sem);
cs1 = current->cpuset;
if (!cs1)
goto done; /* current task exiting */
@@ -1704,7 +1733,7 @@ int cpuset_excl_nodes_overlap(const struct task_struct *p)
cs2 = nearest_exclusive_ancestor(cs2);
overlap = nodes_intersects(cs1->mems_allowed, cs2->mems_allowed);
done:
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
return overlap;
}
@@ -1727,7 +1756,7 @@ static int proc_cpuset_show(struct seq_file *m, void *v)
return -ENOMEM;
tsk = m->private;
- down(&cpuset_sem);
+ cpuset_down(&cpuset_sem);
task_lock(tsk);
cs = tsk->cpuset;
task_unlock(tsk);
@@ -1742,7 +1771,7 @@ static int proc_cpuset_show(struct seq_file *m, void *v)
seq_puts(m, buf);
seq_putc(m, '\n');
out:
- up(&cpuset_sem);
+ cpuset_up(&cpuset_sem);
kfree(buf);
return retval;
}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-19 15:37:10 +0100