From 66d06dffa5ef6f3544997440af63a91ef36a2171 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Sun, 25 Nov 2012 22:48:37 +0100 Subject: [PATCH] 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 Acked-by: Anton Arapov Acked-by: Srikar Dronamraju --- kernel/events/uprobes.c | 51 ++++++++++++----------------------------- 1 file changed, 15 insertions(+), 36 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 358baddc8ac2..c3b65d1c8443 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -50,29 +50,6 @@ static struct rb_root uprobes_tree = RB_ROOT; 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 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer * 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 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume 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 @@ static int __init init_uprobes(void) { 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; -- 2.34.1