uprobes: Document uprobe_register() vs uprobe_mmap() race (c5784de2) · Commits · e / devices / android_kernel_sony_msm8994

kernel/events/uprobes.c

+28 −3

Original line number	Original line	Diff line number	Diff line
	@@ -44,6 +44,23 @@ static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */

	#define UPROBES_HASH_SZ 13		#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 */		/* serialize (un)register */
	static struct mutex uprobes_mutex[UPROBES_HASH_SZ];		static struct mutex uprobes_mutex[UPROBES_HASH_SZ];

	@@ -339,7 +356,9 @@ out:
	int __weak set_swbp(struct arch_uprobe auprobe, struct mm_struct mm, unsigned long vaddr)		int __weak set_swbp(struct arch_uprobe auprobe, struct mm_struct mm, unsigned long vaddr)
	{		{
	int result;		int result;
			/*
			* See the comment near uprobes_hash().
			*/
	result = is_swbp_at_addr(mm, vaddr);		result = is_swbp_at_addr(mm, vaddr);
	if (result == 1)		if (result == 1)
	return -EEXIST;		return -EEXIST;
	@@ -845,6 +864,10 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)

	if (is_register) {		if (is_register) {
	err = install_breakpoint(uprobe, mm, vma, info->vaddr);		err = install_breakpoint(uprobe, mm, vma, info->vaddr);
			/*
			* We can race against uprobe_mmap(), see the
			* comment near uprobe_hash().
			*/
	if (err == -EEXIST)		if (err == -EEXIST)
	err = 0;		err = 0;
	} else {		} else {
	@@ -1054,8 +1077,10 @@ int uprobe_mmap(struct vm_area_struct *vma)
	}		}

	ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);		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) {		if (ret == -EEXIST) {
	ret = 0;		ret = 0;