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>
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@ -50,29 +50,6 @@ static struct rb_root uprobes_tree = RB_ROOT;
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static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */
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#define UPROBES_HASH_SZ 13
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/*
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* We need separate register/unregister and mmap/munmap lock hashes because
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* of mmap_sem nesting.
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*
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* uprobe_register() needs to install probes on (potentially) all processes
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* and thus needs to acquire multiple mmap_sems (consequtively, not
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* concurrently), whereas uprobe_mmap() is called while holding mmap_sem
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* for the particular process doing the mmap.
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*
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* uprobe_register()->register_for_each_vma() needs to drop/acquire mmap_sem
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* because of lock order against i_mmap_mutex. This means there's a hole in
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* the register vma iteration where a mmap() can happen.
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*
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* Thus uprobe_register() can race with uprobe_mmap() and we can try and
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* install a probe where one is already installed.
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*/
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/* serialize (un)register */
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static struct mutex uprobes_mutex[UPROBES_HASH_SZ];
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#define uprobes_hash(v) (&uprobes_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
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/* serialize uprobe->pending_list */
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static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
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#define uprobes_mmap_hash(v) (&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
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@ -865,20 +842,26 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
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if (offset > i_size_read(inode))
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return -EINVAL;
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ret = -ENOMEM;
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mutex_lock(uprobes_hash(inode));
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retry:
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uprobe = alloc_uprobe(inode, offset);
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if (uprobe) {
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down_write(&uprobe->register_rwsem);
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if (!uprobe)
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return -ENOMEM;
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/*
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* We can race with uprobe_unregister()->delete_uprobe().
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* Check uprobe_is_active() and retry if it is false.
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*/
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down_write(&uprobe->register_rwsem);
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ret = -EAGAIN;
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if (likely(uprobe_is_active(uprobe))) {
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ret = __uprobe_register(uprobe, uc);
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if (ret)
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__uprobe_unregister(uprobe, uc);
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up_write(&uprobe->register_rwsem);
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}
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mutex_unlock(uprobes_hash(inode));
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if (uprobe)
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put_uprobe(uprobe);
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up_write(&uprobe->register_rwsem);
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put_uprobe(uprobe);
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if (unlikely(ret == -EAGAIN))
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goto retry;
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return ret;
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}
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@ -896,11 +879,9 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
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if (!uprobe)
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return;
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mutex_lock(uprobes_hash(inode));
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down_write(&uprobe->register_rwsem);
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__uprobe_unregister(uprobe, uc);
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up_write(&uprobe->register_rwsem);
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mutex_unlock(uprobes_hash(inode));
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put_uprobe(uprobe);
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}
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@ -1609,10 +1590,8 @@ static int __init init_uprobes(void)
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{
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int i;
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for (i = 0; i < UPROBES_HASH_SZ; i++) {
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mutex_init(&uprobes_mutex[i]);
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for (i = 0; i < UPROBES_HASH_SZ; i++)
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mutex_init(&uprobes_mmap_mutex[i]);
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}
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if (percpu_init_rwsem(&dup_mmap_sem))
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return -ENOMEM;
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