Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/3] uprobes: install_breakpoint() should fail if is_swbp_insn() == T | From | Peter Zijlstra <> | Date | Wed, 30 May 2012 20:03:36 +0200 |
| |
On Wed, 2012-05-30 at 19:54 +0200, Peter Zijlstra wrote: > Something like so?
--- kernel/events/uprobes.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 985be4d..16f986d 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -45,6 +45,19 @@ 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. + * + * {,un}egister_uprobe() need to install probes on (potentially) all processes + * and thus need to acquire multiple mmap_sems (consequtively, not + * concurrently), whereas uprobe_m{,un}map() are called while holding mmap_sem + * for the particular process doing the mmap. + * + * This all means that register_uprobe() 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]; @@ -356,6 +369,9 @@ int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned { int result; + /* + * See the comment near uprobes_hash(). + */ result = is_swbp_at_addr(mm, vaddr); if (result == 1) return -EEXIST; @@ -870,6 +886,10 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register) up_read(&mm->mmap_sem); mmput(mm); if (is_register) { + /* + * We can race against uprobe_mmap() see the comment + * near uprobe_hash(). + */ if (ret && ret == -EEXIST) ret = 0; if (ret) @@ -1080,7 +1100,10 @@ int uprobe_mmap(struct vm_area_struct *vma) ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr); - /* Ignore double add: */ + /* + * We can race against register_uprobe(), see the + * comment near uprobe_hash(). + */ if (ret == -EEXIST) { ret = 0;
| |