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[ Upstream commitc9287fa657] list_for_each_entry_safe() is not safe for deleting entries from the list if the spin lock, which protects it, is released and reacquired during the list iteration. Fix this issue by replacing this construction with a simple check if list is empty and removing the first entry in each iteration. This is almost equivalent to a revert of the commit mentioned in the Fixes: tag. This patch fixes following issue: --->8--- Unable to handle kernel NULL pointer dereference at virtual address 00000104 pgd = (ptrval) [00000104] *pgd=00000000 Internal error: Oops: 817 [#1] PREEMPT SMP ARM Modules linked in: CPU: 1 PID: 84 Comm: kworker/1:1 Not tainted 4.20.0-rc2-next-20181114-00009-g8266b35ec404 #1061 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree) Workqueue: events eth_work PC is at rx_fill+0x60/0xac LR is at _raw_spin_lock_irqsave+0x50/0x5c pc : [<c065fee0>] lr : [<c0a056b8>] psr: 80000093 sp : ee7fbee8 ip : 00000100 fp : 00000000 r10: 006000c0 r9 : c10b0ab0 r8 : ee7eb5c0 r7 : ee7eb614 r6 : ee7eb5ec r5 : 000000dc r4 : ee12ac00 r3 : ee12ac24 r2 : 00000200 r1 : 60000013 r0 : ee7eb5ec Flags: Nzcv IRQs off FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: 6d5dc04a DAC: 00000051 Process kworker/1:1 (pid: 84, stack limit = 0x(ptrval)) Stack: (0xee7fbee8 to 0xee7fc000) ... [<c065fee0>] (rx_fill) from [<c0143b7c>] (process_one_work+0x200/0x738) [<c0143b7c>] (process_one_work) from [<c0144118>] (worker_thread+0x2c/0x4c8) [<c0144118>] (worker_thread) from [<c014a8a4>] (kthread+0x128/0x164) [<c014a8a4>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xee7fbfb0 to 0xee7fbff8) ... ---[ end trace 64480bc835eba7d6 ]--- Fixes:fea14e68ff("usb: gadget: u_ether: use better list accessors") Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("hub_wq").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.