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Commit e591c8d7 authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Introduce uprobe->register_rwsem 



Introduce uprobe->register_rwsem. It is taken for writing around
__uprobe_register/unregister.

Change handler_chain() to use this sem rather than consumer_rwsem.

The main reason for this change is that we have the nasty problem
with mmap_sem/consumer_rwsem dependency. filter_chain() needs to
protect uprobe->consumers like handler_chain(), but they can not
use the same lock. filter_chain() can be called under ->mmap_sem
(currently this is always true), but we want to allow ->handler()
to play with the probed task's memory, and this needs ->mmap_sem.

Alternatively we could use srcu, but synchronize_srcu() is very
slow and ->register_rwsem allows us to do more. In particular, we
can teach handler_chain() to do remove_breakpoint() if this bp is
"nacked" by all consumers, we know that we can't race with the
new consumer which does uprobe_register().

See also the next patches. uprobes_mutex[] is almost ready to die.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 9a98e03c

kernel/events/uprobes.c

+8 −2
Original line number Diff line number Diff line
@@ -91,6 +91,7 @@ static atomic_t uprobe_events = ATOMIC_INIT(0); 
struct uprobe {

	struct rb_node		rb_node;	/* node in the rb tree */

	atomic_t		ref;

	struct rw_semaphore	register_rwsem;

	struct rw_semaphore	consumer_rwsem;

	struct mutex		copy_mutex;	/* TODO: kill me and UPROBE_COPY_INSN */

	struct list_head	pending_list;
@@ -449,6 +450,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset) 


	uprobe->inode = igrab(inode);

	uprobe->offset = offset;

	init_rwsem(&uprobe->register_rwsem);

	init_rwsem(&uprobe->consumer_rwsem);

	mutex_init(&uprobe->copy_mutex);

	/* For now assume that the instruction need not be single-stepped */
@@ -476,10 +478,10 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) 
	if (!test_bit(UPROBE_RUN_HANDLER, &uprobe->flags))

		return;



	down_read(&uprobe->consumer_rwsem);

	down_read(&uprobe->register_rwsem);

	for (uc = uprobe->consumers; uc; uc = uc->next)

		uc->handler(uc, regs);

	up_read(&uprobe->consumer_rwsem);

	up_read(&uprobe->register_rwsem);

}



static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
@@ -873,9 +875,11 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer * 
	mutex_lock(uprobes_hash(inode));

	uprobe = alloc_uprobe(inode, offset);

	if (uprobe) {

		down_write(&uprobe->register_rwsem);

		ret = __uprobe_register(uprobe, uc);

		if (ret)

			__uprobe_unregister(uprobe, uc);

		up_write(&uprobe->register_rwsem);

	}

	mutex_unlock(uprobes_hash(inode));

	if (uprobe)
@@ -899,7 +903,9 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume 
		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);

}