Messages in this thread | | | Date | Thu, 3 Jan 2013 14:35:56 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH 3/3] uprobes: Kill uprobes_mutex[], separate alloc_uprobe() and __uprobe_register() |
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* Oleg Nesterov <oleg@redhat.com> [2012-11-25 23:33:50]:
> 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: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> --- > kernel/events/uprobes.c | 51 +++++++++++++--------------------------------- > 1 files changed, 15 insertions(+), 36 deletions(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 2886c82..105ac0d 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; > -- > 1.5.5.1 >
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