#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];
int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
{
int result;
-
+ /*
+ * See the comment near uprobes_hash().
+ */
result = is_swbp_at_addr(mm, vaddr);
if (result == 1)
return -EEXIST;
if (is_register) {
err = install_breakpoint(uprobe, mm, vma, info->vaddr);
+ /*
+ * We can race against uprobe_mmap(), see the
+ * comment near uprobe_hash().
+ */
if (err == -EEXIST)
err = 0;
} else {
}
ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
-
- /* Ignore double add: */
+ /*
+ * We can race against uprobe_register(), see the
+ * comment near uprobe_hash().
+ */
if (ret == -EEXIST) {
ret = 0;