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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: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
This commit is contained in:
Oleg Nesterov 2012-11-24 17:29:40 +01:00
parent 9a98e03cc1
commit e591c8d78e
1 changed files with 8 additions and 2 deletions
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10
kernel/events/uprobes.c
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@ -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);
}