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uprobes: Kill uprobes_mutex[], separate alloc_uprobe() and __uprobe_register()

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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>
This commit is contained in:
Oleg Nesterov 2012-11-25 22:48:37 +01:00
parent 06b7bcd8cb
commit 66d06dffa5
1 changed files with 15 additions and 36 deletions
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51
kernel/events/uprobes.c
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@ -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;