Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 159 insertions, 0 deletions

diff --git a/Documentation/PCI/boot-interrupts.rst b/Documentation/PCI/boot-interrupts.rst
new file mode 100644
index 000000000..931077bb0
--- /dev/null
+++ b/Documentation/PCI/boot-interrupts.rst
@@ -0,0 +1,159 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Boot Interrupts
+===============
+
+:Author: - Sean V Kelley <sean.v.kelley@linux.intel.com>
+
+Overview
+========
+
+On PCI Express, interrupts are represented with either MSI or inbound
+interrupt messages (Assert_INTx/Deassert_INTx). The integrated IO-APIC in a
+given Core IO converts the legacy interrupt messages from PCI Express to
+MSI interrupts.  If the IO-APIC is disabled (via the mask bits in the
+IO-APIC table entries), the messages are routed to the legacy PCH. This
+in-band interrupt mechanism was traditionally necessary for systems that
+did not support the IO-APIC and for boot. Intel in the past has used the
+term "boot interrupts" to describe this mechanism. Further, the PCI Express
+protocol describes this in-band legacy wire-interrupt INTx mechanism for
+I/O devices to signal PCI-style level interrupts. The subsequent paragraphs
+describe problems with the Core IO handling of INTx message routing to the
+PCH and mitigation within BIOS and the OS.
+
+
+Issue
+=====
+
+When in-band legacy INTx messages are forwarded to the PCH, they in turn
+trigger a new interrupt for which the OS likely lacks a handler. When an
+interrupt goes unhandled over time, they are tracked by the Linux kernel as
+Spurious Interrupts. The IRQ will be disabled by the Linux kernel after it
+reaches a specific count with the error "nobody cared". This disabled IRQ
+now prevents valid usage by an existing interrupt which may happen to share
+the IRQ line::
+
+  irq 19: nobody cared (try booting with the "irqpoll" option)
+  CPU: 0 PID: 2988 Comm: irq/34-nipalk Tainted: 4.14.87-rt49-02410-g4a640ec-dirty #1
+  Hardware name: National Instruments NI PXIe-8880/NI PXIe-8880, BIOS 2.1.5f1 01/09/2020
+  Call Trace:
+
+  <IRQ>
+   ? dump_stack+0x46/0x5e
+   ? __report_bad_irq+0x2e/0xb0
+   ? note_interrupt+0x242/0x290
+   ? nNIKAL100_memoryRead16+0x8/0x10 [nikal]
+   ? handle_irq_event_percpu+0x55/0x70
+   ? handle_irq_event+0x4f/0x80
+   ? handle_fasteoi_irq+0x81/0x180
+   ? handle_irq+0x1c/0x30
+   ? do_IRQ+0x41/0xd0
+   ? common_interrupt+0x84/0x84
+  </IRQ>
+
+  handlers:
+  irq_default_primary_handler threaded usb_hcd_irq
+  Disabling IRQ #19
+
+
+Conditions
+==========
+
+The use of threaded interrupts is the most likely condition to trigger
+this problem today. Threaded interrupts may not be re-enabled after the IRQ
+handler wakes. These "one shot" conditions mean that the threaded interrupt
+needs to keep the interrupt line masked until the threaded handler has run.
+Especially when dealing with high data rate interrupts, the thread needs to
+run to completion; otherwise some handlers will end up in stack overflows
+since the interrupt of the issuing device is still active.
+
+Affected Chipsets
+=================
+
+The legacy interrupt forwarding mechanism exists today in a number of
+devices including but not limited to chipsets from AMD/ATI, Broadcom, and
+Intel. Changes made through the mitigations below have been applied to
+drivers/pci/quirks.c
+
+Starting with ICX there are no longer any IO-APICs in the Core IO's
+devices.  IO-APIC is only in the PCH.  Devices connected to the Core IO's
+PCIe Root Ports will use native MSI/MSI-X mechanisms.
+
+Mitigations
+===========
+
+The mitigations take the form of PCI quirks. The preference has been to
+first identify and make use of a means to disable the routing to the PCH.
+In such a case a quirk to disable boot interrupt generation can be
+added. [1]_
+
+Intel® 6300ESB I/O Controller Hub
+  Alternate Base Address Register:
+   BIE: Boot Interrupt Enable
+
+	  ==  ===========================
+	  0   Boot interrupt is enabled.
+	  1   Boot interrupt is disabled.
+	  ==  ===========================
+
+Intel® Sandy Bridge through Sky Lake based Xeon servers:
+  Coherent Interface Protocol Interrupt Control
+   dis_intx_route2pch/dis_intx_route2ich/dis_intx_route2dmi2:
+	  When this bit is set. Local INTx messages received from the
+	  Intel® Quick Data DMA/PCI Express ports are not routed to legacy
+	  PCH - they are either converted into MSI via the integrated IO-APIC
+	  (if the IO-APIC mask bit is clear in the appropriate entries)
+	  or cause no further action (when mask bit is set)
+
+In the absence of a way to directly disable the routing, another approach
+has been to make use of PCI Interrupt pin to INTx routing tables for
+purposes of redirecting the interrupt handler to the rerouted interrupt
+line by default.  Therefore, on chipsets where this INTx routing cannot be
+disabled, the Linux kernel will reroute the valid interrupt to its legacy
+interrupt. This redirection of the handler will prevent the occurrence of
+the spurious interrupt detection which would ordinarily disable the IRQ
+line due to excessive unhandled counts. [2]_
+
+The config option X86_REROUTE_FOR_BROKEN_BOOT_IRQS exists to enable (or
+disable) the redirection of the interrupt handler to the PCH interrupt
+line. The option can be overridden by either pci=ioapicreroute or
+pci=noioapicreroute. [3]_
+
+
+More Documentation
+==================
+
+There is an overview of the legacy interrupt handling in several datasheets
+(6300ESB and 6700PXH below). While largely the same, it provides insight
+into the evolution of its handling with chipsets.
+
+Example of disabling of the boot interrupt
+------------------------------------------
+
+      - Intel® 6300ESB I/O Controller Hub (Document # 300641-004US)
+	5.7.3 Boot Interrupt
+	https://www.intel.com/content/dam/doc/datasheet/6300esb-io-controller-hub-datasheet.pdf
+
+      - Intel® Xeon® Processor E5-1600/2400/2600/4600 v3 Product Families
+	Datasheet - Volume 2: Registers (Document # 330784-003)
+	6.6.41 cipintrc Coherent Interface Protocol Interrupt Control
+	https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v3-datasheet-vol-2.pdf
+
+Example of handler rerouting
+----------------------------
+
+      - Intel® 6700PXH 64-bit PCI Hub (Document # 302628)
+	2.15.2 PCI Express Legacy INTx Support and Boot Interrupt
+	https://www.intel.com/content/dam/doc/datasheet/6700pxh-64-bit-pci-hub-datasheet.pdf
+
+
+If you have any legacy PCI interrupt questions that aren't answered, email me.
+
+Cheers,
+    Sean V Kelley
+    sean.v.kelley@linux.intel.com
+
+.. [1] https://lore.kernel.org/r/12131949181903-git-send-email-sassmann@suse.de/
+.. [2] https://lore.kernel.org/r/12131949182094-git-send-email-sassmann@suse.de/
+.. [3] https://lore.kernel.org/r/487C8EA7.6020205@suse.de/