net: buf: Disallow blocking allocation in syswq

Work items on the syswq should always run-to-completion.

Override the timeout value to always be K_NO_WAIT.

Allocating with K_FOREVER leads to deadlocks if the freeing also happens
from the syswq. Non-zero timeouts are also not nice for the other users
of the syswq.

(cherry picked from commit b08b1c2)

Original-Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
GitOrigin-RevId: b08b1c2
Change-Id: Icb45e148317eb510473ddcdfba62126dec5e56e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5482305
Tested-by: Dawid Niedźwiecki <dawidn@google.com>
Commit-Queue: Dawid Niedźwiecki <dawidn@google.com>
Reviewed-by: Dawid Niedźwiecki <dawidn@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>

include/zephyr/net/buf.h

@@ -1315,14 +1315,19 @@ int net_buf_id(struct net_buf *buf);
 /**
  * @brief Allocate a new fixed buffer from a pool.
  *
+ * @note Some types of data allocators do not support
+ *       blocking (such as the HEAP type). In this case it's still possible
+ *       for net_buf_alloc() to fail (return NULL) even if it was given
+ *       K_FOREVER.
+ *
+ * @note The timeout value will be overridden to K_NO_WAIT if called from the
+ *       system workqueue.
+ *
  * @param pool Which pool to allocate the buffer from.
  * @param timeout Affects the action taken should the pool be empty.
  *        If K_NO_WAIT, then return immediately. If K_FOREVER, then
  *        wait as long as necessary. Otherwise, wait until the specified
- *        timeout. Note that some types of data allocators do not support
- *        blocking (such as the HEAP type). In this case it's still possible
- *        for net_buf_alloc() to fail (return NULL) even if it was given
- *        K_FOREVER.
+ *        timeout.
  *
  * @return New buffer or NULL if out of buffers.
  */
@@ -1350,15 +1355,20 @@ static inline struct net_buf * __must_check net_buf_alloc(struct net_buf_pool *p
 /**
  * @brief Allocate a new variable length buffer from a pool.
  *
+ * @note Some types of data allocators do not support
+ *       blocking (such as the HEAP type). In this case it's still possible
+ *       for net_buf_alloc() to fail (return NULL) even if it was given
+ *       K_FOREVER.
+ *
+ * @note The timeout value will be overridden to K_NO_WAIT if called from the
+ *       system workqueue.
+ *
  * @param pool Which pool to allocate the buffer from.
  * @param size Amount of data the buffer must be able to fit.
  * @param timeout Affects the action taken should the pool be empty.
  *        If K_NO_WAIT, then return immediately. If K_FOREVER, then
  *        wait as long as necessary. Otherwise, wait until the specified
- *        timeout. Note that some types of data allocators do not support
- *        blocking (such as the HEAP type). In this case it's still possible
- *        for net_buf_alloc() to fail (return NULL) even if it was given
- *        K_FOREVER.
+ *        timeout.
  *
  * @return New buffer or NULL if out of buffers.
  */
@@ -1382,16 +1392,21 @@ struct net_buf * __must_check net_buf_alloc_len(struct net_buf_pool *pool,
  * Allocate a new buffer from a pool, where the data pointer comes from the
  * user and not from the pool.
  *
+ * @note Some types of data allocators do not support
+ *       blocking (such as the HEAP type). In this case it's still possible
+ *       for net_buf_alloc() to fail (return NULL) even if it was given
+ *       K_FOREVER.
+ *
+ * @note The timeout value will be overridden to K_NO_WAIT if called from the
+ *       system workqueue.
+ *
  * @param pool Which pool to allocate the buffer from.
  * @param data External data pointer
  * @param size Amount of data the pointed data buffer if able to fit.
  * @param timeout Affects the action taken should the pool be empty.
  *        If K_NO_WAIT, then return immediately. If K_FOREVER, then
  *        wait as long as necessary. Otherwise, wait until the specified
- *        timeout. Note that some types of data allocators do not support
- *        blocking (such as the HEAP type). In this case it's still possible
- *        for net_buf_alloc() to fail (return NULL) even if it was given
- *        K_FOREVER.
+ *        timeout.
  *
  * @return New buffer or NULL if out of buffers.
  */

subsys/net/buf.c

@@ -271,6 +271,12 @@ struct net_buf *net_buf_alloc_len(struct net_buf_pool *pool, size_t size,
 
 	k_spin_unlock(&pool->lock, key);
 
+	if (!K_TIMEOUT_EQ(timeout, K_NO_WAIT) &&
+	    k_current_get() == k_work_queue_thread_get(&k_sys_work_q)) {
+		LOG_DBG("Timeout discarded. No blocking in syswq");
+		timeout = K_NO_WAIT;
+	}
+
 #if defined(CONFIG_NET_BUF_LOG) && (CONFIG_NET_BUF_LOG_LEVEL >= LOG_LEVEL_WRN)
 	if (K_TIMEOUT_EQ(timeout, K_FOREVER)) {
 		uint32_t ref = k_uptime_get_32();