uprobes: Kill uprobes_mutex[], separate alloc_uprobe() and __uprobe_register()
uprobe_register() and uprobe_unregister() are the only users of
mutex_lock(uprobes_hash(inode)), and the only reason why we can't
simply remove it is that we need to ensure that delete_uprobe() is
not possible after alloc_uprobe() and before consumer_add().
IOW, we need to ensure that when we take uprobe->register_rwsem
this uprobe is still valid and we didn't race with _unregister()
which called delete_uprobe() in between.
With this patch uprobe_register() simply checks uprobe_is_active()
and retries if it hits this very unlikely race. uprobes_mutex[] is
no longer needed and can be removed.
There is another reason for this change, prepare_uprobe() should be
folded into alloc_uprobe() and we do not want to hold the extra locks
around read_mapping_page/etc.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Anton Arapov <anton@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 358badd..c3b65d1 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -50,29 +50,6 @@
static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */
#define UPROBES_HASH_SZ 13
-
-/*
- * We need separate register/unregister and mmap/munmap lock hashes because
- * of mmap_sem nesting.
- *
- * uprobe_register() needs to install probes on (potentially) all processes
- * and thus needs to acquire multiple mmap_sems (consequtively, not
- * concurrently), whereas uprobe_mmap() is called while holding mmap_sem
- * for the particular process doing the mmap.
- *
- * uprobe_register()->register_for_each_vma() needs to drop/acquire mmap_sem
- * because of lock order against i_mmap_mutex. This means there's a hole in
- * the register vma iteration where a mmap() can happen.
- *
- * Thus uprobe_register() can race with uprobe_mmap() and we can try and
- * install a probe where one is already installed.
- */
-
-/* serialize (un)register */
-static struct mutex uprobes_mutex[UPROBES_HASH_SZ];
-
-#define uprobes_hash(v) (&uprobes_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
-
/* serialize uprobe->pending_list */
static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
#define uprobes_mmap_hash(v) (&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
@@ -865,20 +842,26 @@
if (offset > i_size_read(inode))
return -EINVAL;
- ret = -ENOMEM;
- mutex_lock(uprobes_hash(inode));
+ retry:
uprobe = alloc_uprobe(inode, offset);
- if (uprobe) {
- down_write(&uprobe->register_rwsem);
+ if (!uprobe)
+ return -ENOMEM;
+ /*
+ * We can race with uprobe_unregister()->delete_uprobe().
+ * Check uprobe_is_active() and retry if it is false.
+ */
+ down_write(&uprobe->register_rwsem);
+ ret = -EAGAIN;
+ if (likely(uprobe_is_active(uprobe))) {
ret = __uprobe_register(uprobe, uc);
if (ret)
__uprobe_unregister(uprobe, uc);
- up_write(&uprobe->register_rwsem);
}
- mutex_unlock(uprobes_hash(inode));
- if (uprobe)
- put_uprobe(uprobe);
+ up_write(&uprobe->register_rwsem);
+ put_uprobe(uprobe);
+ if (unlikely(ret == -EAGAIN))
+ goto retry;
return ret;
}
@@ -896,11 +879,9 @@
if (!uprobe)
return;
- mutex_lock(uprobes_hash(inode));
down_write(&uprobe->register_rwsem);
__uprobe_unregister(uprobe, uc);
up_write(&uprobe->register_rwsem);
- mutex_unlock(uprobes_hash(inode));
put_uprobe(uprobe);
}
@@ -1609,10 +1590,8 @@
{
int i;
- for (i = 0; i < UPROBES_HASH_SZ; i++) {
- mutex_init(&uprobes_mutex[i]);
+ for (i = 0; i < UPROBES_HASH_SZ; i++)
mutex_init(&uprobes_mmap_mutex[i]);
- }
if (percpu_init_rwsem(&dup_mmap_sem))
return -ENOMEM;
