USB: gadget: dummy-hcd: Fix wait for outstanding request completions

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The dummy-hcd driver emulates synchronize_irq() by waiting until its
private callback_usage counter drops to 0 (with the private lock not
held).  This counter is incremented whenever a gadget driver callback
occurs (which requires the private lock to be dropped), but not when a
request completion handler is called.

This is an oversight.  Request completion is triggered by timer
interrupts (emulating device IRQs in a real UDC), and the interrupt
handlers are supposed to have completed when the synchronize_irq()
emulation routine returns -- they aren't supposed to be in the middle
of a completion callback.  If this happens it can lead to a gadget
driver's unbind routine running before all outstanding request
completions have finished, maybe even allowing the gadget driver's
module to be unloaded while a completion handler is still running.

Fix the oversight by incrementing the callback_usage value across
request completion callbacks.

Link: https://lore.kernel.org/linux-usb/7a87e293-633c-4100-aa8d-91560ba5e5c5@rowland.harvard.edu/
Fixes: 7dbd8f4cab ("USB: dummy-hcd: Fix erroneous synchronization change")
Tested-by: Minseo Kim <neck3922@gmail.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/f23b9e1a-f110-441a-a1d8-95f442ec09d5@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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Alan Stern 2026-09-20 17:37:34 -04:00 • committed by Greg Kroah-Hartman

parent aef5a7e207

commit b263ff9b0f

1 changed files with 4 additions and 0 deletions

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drivers/usb/gadget/udc/dummy_hcd.c

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