ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 151 insertions, 0 deletions

diff --git a/Documentation/block/null_blk.rst b/Documentation/block/null_blk.rst
new file mode 100644
index 000000000..4dd78f24d
--- /dev/null
+++ b/Documentation/block/null_blk.rst
@@ -0,0 +1,151 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Null block device driver
+========================
+
+Overview
+========
+
+The null block device (``/dev/nullb*``) is used for benchmarking the various
+block-layer implementations. It emulates a block device of X gigabytes in size.
+It does not execute any read/write operation, just mark them as complete in
+the request queue. The following instances are possible:
+
+  Multi-queue block-layer
+
+    - Request-based.
+    - Configurable submission queues per device.
+
+  No block-layer (Known as bio-based)
+
+    - Bio-based. IO requests are submitted directly to the device driver.
+    - Directly accepts bio data structure and returns them.
+
+All of them have a completion queue for each core in the system.
+
+Module parameters
+=================
+
+queue_mode=[0-2]: Default: 2-Multi-queue
+  Selects which block-layer the module should instantiate with.
+
+  =  ============
+  0  Bio-based
+  1  Single-queue (deprecated)
+  2  Multi-queue
+  =  ============
+
+home_node=[0--nr_nodes]: Default: NUMA_NO_NODE
+  Selects what CPU node the data structures are allocated from.
+
+gb=[Size in GB]: Default: 250GB
+  The size of the device reported to the system.
+
+bs=[Block size (in bytes)]: Default: 512 bytes
+  The block size reported to the system.
+
+nr_devices=[Number of devices]: Default: 1
+  Number of block devices instantiated. They are instantiated as /dev/nullb0,
+  etc.
+
+irqmode=[0-2]: Default: 1-Soft-irq
+  The completion mode used for completing IOs to the block-layer.
+
+  =  ===========================================================================
+  0  None.
+  1  Soft-irq. Uses IPI to complete IOs across CPU nodes. Simulates the overhead
+     when IOs are issued from another CPU node than the home the device is
+     connected to.
+  2  Timer: Waits a specific period (completion_nsec) for each IO before
+     completion.
+  =  ===========================================================================
+
+completion_nsec=[ns]: Default: 10,000ns
+  Combined with irqmode=2 (timer). The time each completion event must wait.
+
+submit_queues=[1..nr_cpus]: Default: 1
+  The number of submission queues attached to the device driver. If unset, it
+  defaults to 1. For multi-queue, it is ignored when use_per_node_hctx module
+  parameter is 1.
+
+hw_queue_depth=[0..qdepth]: Default: 64
+  The hardware queue depth of the device.
+
+memory_backed=[0/1]: Default: 0
+  Whether or not to use a memory buffer to respond to IO requests
+
+  =  =============================================
+  0  Transfer no data in response to IO requests
+  1  Use a memory buffer to respond to IO requests
+  =  =============================================
+
+discard=[0/1]: Default: 0
+  Support discard operations (requires memory-backed null_blk device).
+
+  =  =====================================
+  0  Do not support discard operations
+  1  Enable support for discard operations
+  =  =====================================
+
+cache_size=[Size in MB]: Default: 0
+  Cache size in MB for memory-backed device.
+
+mbps=[Maximum bandwidth in MB/s]: Default: 0 (no limit)
+  Bandwidth limit for device performance.
+
+Multi-queue specific parameters
+-------------------------------
+
+use_per_node_hctx=[0/1]: Default: 0
+  Number of hardware context queues.
+
+  =  =====================================================================
+  0  The number of submit queues are set to the value of the submit_queues
+     parameter.
+  1  The multi-queue block layer is instantiated with a hardware dispatch
+     queue for each CPU node in the system.
+  =  =====================================================================
+
+no_sched=[0/1]: Default: 0
+  Enable/disable the io scheduler.
+
+  =  ======================================
+  0  nullb* use default blk-mq io scheduler
+  1  nullb* doesn't use io scheduler
+  =  ======================================
+
+blocking=[0/1]: Default: 0
+  Blocking behavior of the request queue.
+
+  =  ===============================================================
+  0  Register as a non-blocking blk-mq driver device.
+  1  Register as a blocking blk-mq driver device, null_blk will set
+     the BLK_MQ_F_BLOCKING flag, indicating that it sometimes/always
+     needs to block in its ->queue_rq() function.
+  =  ===============================================================
+
+shared_tags=[0/1]: Default: 0
+  Sharing tags between devices.
+
+  =  ================================================================
+  0  Tag set is not shared.
+  1  Tag set shared between devices for blk-mq. Only makes sense with
+     nr_devices > 1, otherwise there's no tag set to share.
+  =  ================================================================
+
+zoned=[0/1]: Default: 0
+  Device is a random-access or a zoned block device.
+
+  =  ======================================================================
+  0  Block device is exposed as a random-access block device.
+  1  Block device is exposed as a host-managed zoned block device. Requires
+     CONFIG_BLK_DEV_ZONED.
+  =  ======================================================================
+
+zone_size=[MB]: Default: 256
+  Per zone size when exposed as a zoned block device. Must be a power of two.
+
+zone_nr_conv=[nr_conv]: Default: 0
+  The number of conventional zones to create when block device is zoned.  If
+  zone_nr_conv >= nr_zones, it will be reduced to nr_zones - 1.