Re: FAILED: patch "[PATCH] usb: dwc3: gadget: Use list_replace_init() before traversing" failed to apply to 5.10-stable tree

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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Hi Greg,

On Mon, Aug 09, 2021 at 10:48:22AM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.10-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Here is the backport, will also apply to 5.4-stable and 4.19-stable.

--
Regards
Sudip

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From e01c2051bac15d89168e30c2cfa2cd828104ed4d Mon Sep 17 00:00:00 2001
From: Wesley Cheng <wcheng@codeaurora.org>
Date: Thu, 29 Jul 2021 00:33:14 -0700
Subject: [PATCH] usb: dwc3: gadget: Use list_replace_init() before traversing
 lists

commit d25d85061bd856d6be221626605319154f9b5043 upstream

The list_for_each_entry_safe() macro saves the current item (n) and
the item after (n+1), so that n can be safely removed without
corrupting the list.  However, when traversing the list and removing
items using gadget giveback, the DWC3 lock is briefly released,
allowing other routines to execute.  There is a situation where, while
items are being removed from the cancelled_list using
dwc3_gadget_ep_cleanup_cancelled_requests(), the pullup disable
routine is running in parallel (due to UDC unbind).  As the cleanup
routine removes n, and the pullup disable removes n+1, once the
cleanup retakes the DWC3 lock, it references a request who was already
removed/handled.  With list debug enabled, this leads to a panic.
Ensure all instances of the macro are replaced where gadget giveback
is used.

Example call stack:

Thread#1:
__dwc3_gadget_ep_set_halt() - CLEAR HALT
  -> dwc3_gadget_ep_cleanup_cancelled_requests()
    ->list_for_each_entry_safe()
    ->dwc3_gadget_giveback(n)
      ->dwc3_gadget_del_and_unmap_request()- n deleted[cancelled_list]
      ->spin_unlock
      ->Thread#2 executes
      ...
    ->dwc3_gadget_giveback(n+1)
      ->Already removed!

Thread#2:
dwc3_gadget_pullup()
  ->waiting for dwc3 spin_lock
  ...
  ->Thread#1 released lock
  ->dwc3_stop_active_transfers()
    ->dwc3_remove_requests()
      ->fetches n+1 item from cancelled_list (n removed by Thread#1)
      ->dwc3_gadget_giveback()
        ->dwc3_gadget_del_and_unmap_request()- n+1
deleted[cancelled_list]
        ->spin_unlock

Fix this condition by utilizing list_replace_init(), and traversing
through a local copy of the current elements in the endpoint lists.
This will also set the parent list as empty, so if another thread is
also looping through the list, it will be empty on the next iteration.

Fixes: d4f1afe5e896 ("usb: dwc3: gadget: move requests to cancelled_list")
Cc: stable <stable@vger.kernel.org>
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/1627543994-20327-1-git-send-email-wcheng@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
---
 drivers/usb/dwc3/gadget.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 756839e0e91d..788bbb38cf79 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1733,11 +1733,18 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
 {
 	struct dwc3_request		*req;
 	struct dwc3_request		*tmp;
+	struct list_head		local;
 
-	list_for_each_entry_safe(req, tmp, &dep->cancelled_list, list) {
+restart:
+	list_replace_init(&dep->cancelled_list, &local);
+
+	list_for_each_entry_safe(req, tmp, &local, list) {
 		dwc3_gadget_ep_skip_trbs(dep, req);
 		dwc3_gadget_giveback(dep, req, -ECONNRESET);
 	}
+
+	if (!list_empty(&dep->cancelled_list))
+		goto restart;
 }
 
 static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
@@ -2867,8 +2874,12 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
 {
 	struct dwc3_request	*req;
 	struct dwc3_request	*tmp;
+	struct list_head	local;
 
-	list_for_each_entry_safe(req, tmp, &dep->started_list, list) {
+restart:
+	list_replace_init(&dep->started_list, &local);
+
+	list_for_each_entry_safe(req, tmp, &local, list) {
 		int ret;
 
 		ret = dwc3_gadget_ep_cleanup_completed_request(dep, event,
@@ -2876,6 +2887,9 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
 		if (ret)
 			break;
 	}
+
+	if (!list_empty(&dep->started_list))
+		goto restart;
 }
 
 static bool dwc3_gadget_ep_should_continue(struct dwc3_ep *dep)
-- 
2.30.2