* [PATCH] net: qrtr: ns: Fix the incorrect usage of rcu_read_lock()
@ 2020-10-02 14:15 Manivannan Sadhasivam
2020-10-02 15:28 ` Doug Anderson
0 siblings, 1 reply; 3+ messages in thread
From: Manivannan Sadhasivam @ 2020-10-02 14:15 UTC (permalink / raw)
To: davem, kuba
Cc: bjorn.andersson, netdev, linux-kernel, dianders, elder,
Manivannan Sadhasivam
The rcu_read_lock() is not supposed to lock the kernel_sendmsg() API
since it has the lock_sock() in qrtr_sendmsg() which will sleep. Hence,
fix it by excluding the locking for kernel_sendmsg().
Fixes: a7809ff90ce6 ("net: qrtr: ns: Protect radix_tree_deref_slot() using rcu read locks")
Reported-by: Doug Anderson <dianders@chromium.org>
Tested-by: Alex Elder <elder@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
net/qrtr/ns.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/net/qrtr/ns.c b/net/qrtr/ns.c
index 934999b56d60..0515433de922 100644
--- a/net/qrtr/ns.c
+++ b/net/qrtr/ns.c
@@ -203,15 +203,17 @@ static int announce_servers(struct sockaddr_qrtr *sq)
/* Announce the list of servers registered in this node */
radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
srv = radix_tree_deref_slot(slot);
+ rcu_read_unlock();
ret = service_announce_new(sq, srv);
if (ret < 0) {
pr_err("failed to announce new service\n");
- goto err_out;
+ return ret;
}
+
+ rcu_read_lock();
}
-err_out:
rcu_read_unlock();
return ret;
@@ -352,7 +354,9 @@ static int ctrl_cmd_bye(struct sockaddr_qrtr *from)
/* Advertise removal of this client to all servers of remote node */
radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
srv = radix_tree_deref_slot(slot);
+ rcu_read_unlock();
server_del(node, srv->port);
+ rcu_read_lock();
}
rcu_read_unlock();
@@ -368,6 +372,7 @@ static int ctrl_cmd_bye(struct sockaddr_qrtr *from)
rcu_read_lock();
radix_tree_for_each_slot(slot, &local_node->servers, &iter, 0) {
srv = radix_tree_deref_slot(slot);
+ rcu_read_unlock();
sq.sq_family = AF_QIPCRTR;
sq.sq_node = srv->node;
@@ -379,11 +384,11 @@ static int ctrl_cmd_bye(struct sockaddr_qrtr *from)
ret = kernel_sendmsg(qrtr_ns.sock, &msg, &iv, 1, sizeof(pkt));
if (ret < 0) {
pr_err("failed to send bye cmd\n");
- goto err_out;
+ return ret;
}
+ rcu_read_lock();
}
-err_out:
rcu_read_unlock();
return ret;
@@ -447,6 +452,7 @@ static int ctrl_cmd_del_client(struct sockaddr_qrtr *from,
rcu_read_lock();
radix_tree_for_each_slot(slot, &local_node->servers, &iter, 0) {
srv = radix_tree_deref_slot(slot);
+ rcu_read_unlock();
sq.sq_family = AF_QIPCRTR;
sq.sq_node = srv->node;
@@ -458,11 +464,11 @@ static int ctrl_cmd_del_client(struct sockaddr_qrtr *from,
ret = kernel_sendmsg(qrtr_ns.sock, &msg, &iv, 1, sizeof(pkt));
if (ret < 0) {
pr_err("failed to send del client cmd\n");
- goto err_out;
+ return ret;
}
+ rcu_read_lock();
}
-err_out:
rcu_read_unlock();
return ret;
@@ -580,7 +586,9 @@ static int ctrl_cmd_new_lookup(struct sockaddr_qrtr *from,
if (!server_match(srv, &filter))
continue;
+ rcu_read_unlock();
lookup_notify(from, srv, true);
+ rcu_read_lock();
}
}
rcu_read_unlock();
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] net: qrtr: ns: Fix the incorrect usage of rcu_read_lock()
2020-10-02 14:15 [PATCH] net: qrtr: ns: Fix the incorrect usage of rcu_read_lock() Manivannan Sadhasivam
@ 2020-10-02 15:28 ` Doug Anderson
2020-10-02 16:04 ` Manivannan Sadhasivam
0 siblings, 1 reply; 3+ messages in thread
From: Doug Anderson @ 2020-10-02 15:28 UTC (permalink / raw)
To: Manivannan Sadhasivam
Cc: David Miller, Jakub Kicinski, Bjorn Andersson, netdev, LKML, Alex Elder
Hi,
On Fri, Oct 2, 2020 at 7:15 AM Manivannan Sadhasivam
<manivannan.sadhasivam@linaro.org> wrote:
>
> The rcu_read_lock() is not supposed to lock the kernel_sendmsg() API
> since it has the lock_sock() in qrtr_sendmsg() which will sleep. Hence,
> fix it by excluding the locking for kernel_sendmsg().
>
> Fixes: a7809ff90ce6 ("net: qrtr: ns: Protect radix_tree_deref_slot() using rcu read locks")
> Reported-by: Doug Anderson <dianders@chromium.org>
> Tested-by: Alex Elder <elder@linaro.org>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
> net/qrtr/ns.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/net/qrtr/ns.c b/net/qrtr/ns.c
> index 934999b56d60..0515433de922 100644
> --- a/net/qrtr/ns.c
> +++ b/net/qrtr/ns.c
> @@ -203,15 +203,17 @@ static int announce_servers(struct sockaddr_qrtr *sq)
> /* Announce the list of servers registered in this node */
> radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
> srv = radix_tree_deref_slot(slot);
> + rcu_read_unlock();
My RCU-fu is mediocre at best and my radix-tree knowledge is
non-existent. However:
=> Reading through radix_tree_deref_slot() it says that if you are
only holding the read lock that you need to be calling
radix_tree_deref_retry(). Why don't I see that here?
=> Without any real knowledge, it seems super sketchy to drop the lock
while iterating over the tree. Somehow that feels unsafe. Hrm, there
seems to be a function radix_tree_iter_resume() that might be exactly
what you want, but I'm not totally sure. The only user I can see
in-tree (other than radix tree regression testing) is btrfs-tests.c
but it's using it together with radix_tree_deref_slot_protected().
In any case, my totally untested and totally knowedge-free proposal
would look something like this:
rcu_read_lock();
/* Announce the list of servers registered in this node */
radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
srv = radix_tree_deref_slot(slot);
if (!srv)
continue;
if (radix_tree_deref_retry(srv)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
slot = radix_tree_iter_resume(slot, &iter);
rcu_read_unlock();
ret = service_announce_new(sq, srv);
if (ret < 0) {
pr_err("failed to announce new service\n");
return ret;
}
rcu_read_lock();
}
rcu_read_unlock();
What a beast! Given that this doesn't seem to be what anyone else in
the kernel is doing exactly, it makes me suspect that there's a more
fundamental design issue here, though...
-Doug
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] net: qrtr: ns: Fix the incorrect usage of rcu_read_lock()
2020-10-02 15:28 ` Doug Anderson
@ 2020-10-02 16:04 ` Manivannan Sadhasivam
0 siblings, 0 replies; 3+ messages in thread
From: Manivannan Sadhasivam @ 2020-10-02 16:04 UTC (permalink / raw)
To: Doug Anderson
Cc: David Miller, Jakub Kicinski, Bjorn Andersson, netdev, LKML, Alex Elder
Hi Doug,
On Fri, Oct 02, 2020 at 08:28:51AM -0700, Doug Anderson wrote:
> Hi,
>
> On Fri, Oct 2, 2020 at 7:15 AM Manivannan Sadhasivam
> <manivannan.sadhasivam@linaro.org> wrote:
> >
> > The rcu_read_lock() is not supposed to lock the kernel_sendmsg() API
> > since it has the lock_sock() in qrtr_sendmsg() which will sleep. Hence,
> > fix it by excluding the locking for kernel_sendmsg().
> >
> > Fixes: a7809ff90ce6 ("net: qrtr: ns: Protect radix_tree_deref_slot() using rcu read locks")
> > Reported-by: Doug Anderson <dianders@chromium.org>
> > Tested-by: Alex Elder <elder@linaro.org>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > ---
> > net/qrtr/ns.c | 20 ++++++++++++++------
> > 1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/net/qrtr/ns.c b/net/qrtr/ns.c
> > index 934999b56d60..0515433de922 100644
> > --- a/net/qrtr/ns.c
> > +++ b/net/qrtr/ns.c
> > @@ -203,15 +203,17 @@ static int announce_servers(struct sockaddr_qrtr *sq)
> > /* Announce the list of servers registered in this node */
> > radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
> > srv = radix_tree_deref_slot(slot);
> > + rcu_read_unlock();
>
> My RCU-fu is mediocre at best and my radix-tree knowledge is
> non-existent. However:
>
> => Reading through radix_tree_deref_slot() it says that if you are
> only holding the read lock that you need to be calling
> radix_tree_deref_retry(). Why don't I see that here?
>
Well, I drew inspiration from peer drivers and didn't look into the API
documentation properly, my bad :(
> => Without any real knowledge, it seems super sketchy to drop the lock
> while iterating over the tree. Somehow that feels unsafe. Hrm, there
> seems to be a function radix_tree_iter_resume() that might be exactly
> what you want, but I'm not totally sure. The only user I can see
> in-tree (other than radix tree regression testing) is btrfs-tests.c
> but it's using it together with radix_tree_deref_slot_protected().
>
> In any case, my totally untested and totally knowedge-free proposal
> would look something like this:
>
> rcu_read_lock();
> /* Announce the list of servers registered in this node */
> radix_tree_for_each_slot(slot, &node->servers, &iter, 0) {
> srv = radix_tree_deref_slot(slot);
> if (!srv)
> continue;
> if (radix_tree_deref_retry(srv)) {
> slot = radix_tree_iter_retry(&iter);
> continue;
> }
> slot = radix_tree_iter_resume(slot, &iter);
> rcu_read_unlock();
>
> ret = service_announce_new(sq, srv);
> if (ret < 0) {
> pr_err("failed to announce new service\n");
> return ret;
> }
>
> rcu_read_lock();
> }
>
> rcu_read_unlock();
>
> What a beast! Given that this doesn't seem to be what anyone else in
> the kernel is doing exactly, it makes me suspect that there's a more
> fundamental design issue here, though...
>
That's how it is supposed to be. So I'm going to roll out next revision with
your suggestion for the rest of the deref_slot() calls also.
Thanks for your time looking into this.
Regards,
Mani
> -Doug
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-10-02 14:15 [PATCH] net: qrtr: ns: Fix the incorrect usage of rcu_read_lock() Manivannan Sadhasivam
2020-10-02 15:28 ` Doug Anderson
2020-10-02 16:04 ` Manivannan Sadhasivam
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