* Oleg Nesterov <o...@redhat.com> [2012-11-24 19:02:28]:
> 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: Oleg Nesterov <o...@redhat.com>
Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> ---
> kernel/events/uprobes.c | 10 ++++++++--
> 1 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index c80507d..03ffbb5 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -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);
> }
> --
> 1.5.5.1
>
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