[PATCH 5.10 081/199] RDMA/ucma: Do not miss ctx destruction steps in some cases

Greg Kroah-Hartman
2021-01-26T09:38:01Z

From: Jason Gunthorpe <jgg@nvidia.com>

[ Upstream commit 8ae291cc95e49011b736b641b0cfad502b7a1526 ]

The destruction flow is very complicated here because the cm_id can be
destroyed from the event handler at any time if the device is
hot-removed. This leaves behind a partial ctx with no cm_id in the
xarray, and will let user space leak memory.

Make everything consistent in this flow in all places:

- Return the xarray back to XA_ZERO_ENTRY before beginning any
destruction. The thread that reaches this first is responsible to
kfree, everyone else does nothing.

- Test the xarray during the special hot-removal case to block the
queue_work, this has much simpler locking and doesn't require a
'destroying'

- Fix the ref initialization so that it is only positive if cm_id !=
NULL, then rely on that to guide the destruction process in all cases.

Now the new ucma_destroy_private_ctx() can be called in all places that
want to free the ctx, including all the error unwinds, and none of the
details are missed.

Fixes: a1d33b70dbbc ("RDMA/ucma: Rework how new connections are passed through event delivery")
Link: https://lore.kernel.org/r/20210105111327.230270-1-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/infiniband/core/ucma.c | 135 ++++++++++++++++++---------------
1 file changed, 72 insertions(+), 63 deletions(-)

diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index ffe2563ad3456..2cc785c1970b4 100644
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -95,8 +95,6 @@ struct ucma_context {
u64 uid;

struct list_head list;
- /* sync between removal event and id destroy, protected by file mut */
- int destroying;
struct work_struct close_work;
};

@@ -122,7 +120,7 @@ static DEFINE_XARRAY_ALLOC(ctx_table);
static DEFINE_XARRAY_ALLOC(multicast_table);

static const struct file_operations ucma_fops;
-static int __destroy_id(struct ucma_context *ctx);
+static int ucma_destroy_private_ctx(struct ucma_context *ctx);

static inline struct ucma_context *_ucma_find_context(int id,
struct ucma_file *file)
@@ -179,19 +177,14 @@ static void ucma_close_id(struct work_struct *work)

/* once all inflight tasks are finished, we close all underlying
* resources. The context is still alive till its explicit destryoing
- * by its creator.
+ * by its creator. This puts back the xarray's reference.
*/
ucma_put_ctx(ctx);
wait_for_completion(&ctx->comp);
/* No new events will be generated after destroying the id. */
rdma_destroy_id(ctx->cm_id);

- /*
- * At this point ctx->ref is zero so the only place the ctx can be is in
- * a uevent or in __destroy_id(). Since the former doesn't touch
- * ctx->cm_id and the latter sync cancels this, there is no races with
- * this store.
- */
+ /* Reading the cm_id without holding a positive ref is not allowed */
ctx->cm_id = NULL;
}

@@ -204,7 +197,6 @@ static struct ucma_context *ucma_alloc_ctx(struct ucma_file *file)
return NULL;

INIT_WORK(&ctx->close_work, ucma_close_id);
- refcount_set(&ctx->ref, 1);
init_completion(&ctx->comp);
/* So list_del() will work if we don't do ucma_finish_ctx() */
INIT_LIST_HEAD(&ctx->list);
@@ -218,6 +210,13 @@ static struct ucma_context *ucma_alloc_ctx(struct ucma_file *file)
return ctx;
}

+static void ucma_set_ctx_cm_id(struct ucma_context *ctx,
+ struct rdma_cm_id *cm_id)
+{
+ refcount_set(&ctx->ref, 1);
+ ctx->cm_id = cm_id;
+}
+
static void ucma_finish_ctx(struct ucma_context *ctx)
{
lockdep_assert_held(&ctx->file->mut);
@@ -303,7 +302,7 @@ static int ucma_connect_event_handler(struct rdma_cm_id *cm_id,
ctx = ucma_alloc_ctx(listen_ctx->file);
if (!ctx)
goto err_backlog;
- ctx->cm_id = cm_id;
+ ucma_set_ctx_cm_id(ctx, cm_id);

uevent = ucma_create_uevent(listen_ctx, event);
if (!uevent)
@@ -321,8 +320,7 @@ static int ucma_connect_event_handler(struct rdma_cm_id *cm_id,
return 0;

err_alloc:
- xa_erase(&ctx_table, ctx->id);
- kfree(ctx);
+ ucma_destroy_private_ctx(ctx);
err_backlog:
atomic_inc(&listen_ctx->backlog);
/* Returning error causes the new ID to be destroyed */
@@ -356,8 +354,12 @@ static int ucma_event_handler(struct rdma_cm_id *cm_id,
wake_up_interruptible(&ctx->file->poll_wait);
}

- if (event->event == RDMA_CM_EVENT_DEVICE_REMOVAL && !ctx->destroying)
- queue_work(system_unbound_wq, &ctx->close_work);
+ if (event->event == RDMA_CM_EVENT_DEVICE_REMOVAL) {
+ xa_lock(&ctx_table);
+ if (xa_load(&ctx_table, ctx->id) == ctx)
+ queue_work(system_unbound_wq, &ctx->close_work);
+ xa_unlock(&ctx_table);
+ }
return 0;
}

@@ -461,13 +463,12 @@ static ssize_t ucma_create_id(struct ucma_file *file, const char __user *inbuf,
ret = PTR_ERR(cm_id);
goto err1;
}
- ctx->cm_id = cm_id;
+ ucma_set_ctx_cm_id(ctx, cm_id);

resp.id = ctx->id;
if (copy_to_user(u64_to_user_ptr(cmd.response),
&resp, sizeof(resp))) {
- xa_erase(&ctx_table, ctx->id);
- __destroy_id(ctx);
+ ucma_destroy_private_ctx(ctx);
return -EFAULT;
}

@@ -477,8 +478,7 @@ static ssize_t ucma_create_id(struct ucma_file *file, const char __user *inbuf,
return 0;

err1:
- xa_erase(&ctx_table, ctx->id);
- kfree(ctx);
+ ucma_destroy_private_ctx(ctx);
return ret;
}

@@ -516,68 +516,73 @@ static void ucma_cleanup_mc_events(struct ucma_multicast *mc)
rdma_unlock_handler(mc->ctx->cm_id);
}

-/*
- * ucma_free_ctx is called after the underlying rdma CM-ID is destroyed. At
- * this point, no new events will be reported from the hardware. However, we
- * still need to cleanup the UCMA context for this ID. Specifically, there
- * might be events that have not yet been consumed by the user space software.
- * mutex. After that we release them as needed.
- */
-static int ucma_free_ctx(struct ucma_context *ctx)
+static int ucma_cleanup_ctx_events(struct ucma_context *ctx)
{
int events_reported;
struct ucma_event *uevent, *tmp;
LIST_HEAD(list);

- ucma_cleanup_multicast(ctx);
-
- /* Cleanup events not yet reported to the user. */
+ /* Cleanup events not yet reported to the user.*/
mutex_lock(&ctx->file->mut);
list_for_each_entry_safe(uevent, tmp, &ctx->file->event_list, list) {
- if (uevent->ctx == ctx || uevent->conn_req_ctx == ctx)
+ if (uevent->ctx != ctx)
+ continue;
+
+ if (uevent->resp.event == RDMA_CM_EVENT_CONNECT_REQUEST &&
+ xa_cmpxchg(&ctx_table, uevent->conn_req_ctx->id,
+ uevent->conn_req_ctx, XA_ZERO_ENTRY,
+ GFP_KERNEL) == uevent->conn_req_ctx) {
list_move_tail(&uevent->list, &list);
+ continue;
+ }
+ list_del(&uevent->list);
+ kfree(uevent);
}
list_del(&ctx->list);
events_reported = ctx->events_reported;
mutex_unlock(&ctx->file->mut);

/*
- * If this was a listening ID then any connections spawned from it
- * that have not been delivered to userspace are cleaned up too.
- * Must be done outside any locks.
+ * If this was a listening ID then any connections spawned from it that
+ * have not been delivered to userspace are cleaned up too. Must be done
+ * outside any locks.
*/
list_for_each_entry_safe(uevent, tmp, &list, list) {
- list_del(&uevent->list);
- if (uevent->resp.event == RDMA_CM_EVENT_CONNECT_REQUEST &&
- uevent->conn_req_ctx != ctx)
- __destroy_id(uevent->conn_req_ctx);
+ ucma_destroy_private_ctx(uevent->conn_req_ctx);
kfree(uevent);
}
-
- mutex_destroy(&ctx->mutex);
- kfree(ctx);
return events_reported;
}

-static int __destroy_id(struct ucma_context *ctx)
+/*
+ * When this is called the xarray must have a XA_ZERO_ENTRY in the ctx->id (ie
+ * the ctx is not public to the user). This either because:
+ * - ucma_finish_ctx() hasn't been called
+ * - xa_cmpxchg() succeed to remove the entry (only one thread can succeed)
+ */
+static int ucma_destroy_private_ctx(struct ucma_context *ctx)
{
+ int events_reported;
+
/*
- * If the refcount is already 0 then ucma_close_id() has already
- * destroyed the cm_id, otherwise holding the refcount keeps cm_id
- * valid. Prevent queue_work() from being called.
+ * Destroy the underlying cm_id. New work queuing is prevented now by
+ * the removal from the xarray. Once the work is cancled ref will either
+ * be 0 because the work ran to completion and consumed the ref from the
+ * xarray, or it will be positive because we still have the ref from the
+ * xarray. This can also be 0 in cases where cm_id was never set
*/
- if (refcount_inc_not_zero(&ctx->ref)) {
- rdma_lock_handler(ctx->cm_id);
- ctx->destroying = 1;
- rdma_unlock_handler(ctx->cm_id);
- ucma_put_ctx(ctx);
- }
-
cancel_work_sync(&ctx->close_work);
- /* At this point it's guaranteed that there is no inflight closing task */
- if (ctx->cm_id)
+ if (refcount_read(&ctx->ref))
ucma_close_id(&ctx->close_work);
- return ucma_free_ctx(ctx);
+
+ events_reported = ucma_cleanup_ctx_events(ctx);
+ ucma_cleanup_multicast(ctx);
+
+ WARN_ON(xa_cmpxchg(&ctx_table, ctx->id, XA_ZERO_ENTRY, NULL,
+ GFP_KERNEL) != NULL);
+ mutex_destroy(&ctx->mutex);
+ kfree(ctx);
+ return events_reported;
}

static ssize_t ucma_destroy_id(struct ucma_file *file, const char __user *inbuf,
@@ -596,14 +601,17 @@ static ssize_t ucma_destroy_id(struct ucma_file *file, const char __user *inbuf,

xa_lock(&ctx_table);
ctx = _ucma_find_context(cmd.id, file);
- if (!IS_ERR(ctx))
- __xa_erase(&ctx_table, ctx->id);
+ if (!IS_ERR(ctx)) {
+ if (__xa_cmpxchg(&ctx_table, ctx->id, ctx, XA_ZERO_ENTRY,
+ GFP_KERNEL) != ctx)
+ ctx = ERR_PTR(-ENOENT);
+ }
xa_unlock(&ctx_table);

if (IS_ERR(ctx))
return PTR_ERR(ctx);

- resp.events_reported = __destroy_id(ctx);
+ resp.events_reported = ucma_destroy_private_ctx(ctx);
if (copy_to_user(u64_to_user_ptr(cmd.response),
&resp, sizeof(resp)))
ret = -EFAULT;
@@ -1777,15 +1785,16 @@ static int ucma_close(struct inode *inode, struct file *filp)
* prevented by this being a FD release function. The list_add_tail() in
* ucma_connect_event_handler() can run concurrently, however it only
* adds to the list *after* a listening ID. By only reading the first of
- * the list, and relying on __destroy_id() to block
+ * the list, and relying on ucma_destroy_private_ctx() to block
* ucma_connect_event_handler(), no additional locking is needed.
*/
while (!list_empty(&file->ctx_list)) {
struct ucma_context *ctx = list_first_entry(
&file->ctx_list, struct ucma_context, list);

- xa_erase(&ctx_table, ctx->id);
- __destroy_id(ctx);
+ WARN_ON(xa_cmpxchg(&ctx_table, ctx->id, ctx, XA_ZERO_ENTRY,
+ GFP_KERNEL) != ctx);
+ ucma_destroy_private_ctx(ctx);
}
kfree(file);
return 0;
--
2.27.0