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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Dec 2025 15:04:13.7073 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 308bca0d-2f22-4330-d3bf-08de3cb46025 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB1PEPF00039231.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1PR08MB5741 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251216_070424_088732_D0E158CC X-CRM114-Status: GOOD ( 25.59 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Simon, > On Fri, Dec 12, 2025 at 07:03:38PM +0000, Yeoreum Yun wrote: > > When smc91x.c is built with PREEMPT_RT, the following splat occurs > > in FVP_RevC: > > > > [ 13.055000] smc91x LNRO0003:00 eth0: link up, 10Mbps, half-duplex, lpa 0x0000 > > [ 13.062137] BUG: workqueue leaked atomic, lock or RCU: kworker/2:1[106] > > [ 13.062137] preempt=0x00000000 lock=0->0 RCU=0->1 workfn=mld_ifc_work > > [ 13.062266] C > > ** replaying previous printk message ** > > [ 13.062266] CPU: 2 UID: 0 PID: 106 Comm: kworker/2:1 Not tainted 6.18.0-dirty #179 PREEMPT_{RT,(full)} > > [ 13.062353] Hardware name: , BIOS > > [ 13.062382] Workqueue: mld mld_ifc_work > > [ 13.062469] Call trace: > > [ 13.062494] show_stack+0x24/0x40 (C) > > [ 13.062602] __dump_stack+0x28/0x48 > > [ 13.062710] dump_stack_lvl+0x7c/0xb0 > > [ 13.062818] dump_stack+0x18/0x34 > > [ 13.062926] process_scheduled_works+0x294/0x450 > > [ 13.063043] worker_thread+0x260/0x3d8 > > [ 13.063124] kthread+0x1c4/0x228 > > [ 13.063235] ret_from_fork+0x10/0x20 > > > > This happens because smc_special_trylock() disables IRQs even on PREEMPT_RT, > > but smc_special_unlock() does not restore IRQs on PREEMPT_RT. > > The reason is that smc_special_unlock() calls spin_unlock_irqrestore(), > > and rcu_read_unlock_bh() in __dev_queue_xmit() cannot invoke > > rcu_read_unlock() through __local_bh_enable_ip() when current->softirq_disable_cnt becomes zero. > > > > To address this issue, replace smc_special_trylock() with spin_trylock_irqsave(). > > > > Fixes: 8ff499e43c53 ("smc91x: let smc91x work well under netpoll") > > Signed-off-by: Yeoreum Yun > > --- > > This patch based on v6.18. > > > > History > > ======== > > > > >From v1 to v2: > > - remove debug log. > > - https://lore.kernel.org/all/20251212185818.2209573-1-yeoreum.yun@arm.com/ > > > > Firstly, I'd like to note that it seems to me that the last > non-trivial update to this driver seems to have occurred back in 2016. > Do you know if it is still actively used? Unfortunately, I don't know whether it is still actively used in real. AFAIK it could be used in qemu or arm FVP... > > I agree that this patch seems appropriate as a bug fix. > But I do wonder if, as a follow-up for net-next when it re-opens, > smc_special_*lock could be removed entirely. > Other than being the source of this bug (which I guess is special), > they don't seem very special anymore. Perhaps they were once, > but that time seems to have passed. IIUC, remove smc_special*_lock() and replace them with "spin_*lock_*" right? If so, It seems good. Even UP case, I think it seems better to protect critical section in smc_hardware_send_pkt() and smc_hard_start_xmit() with spin_lock_irqsave() from interrupt handler. > > Regarding the Fixes tag. I wonder if this one, which post-dates the > currently cited commit is correct. It seems to be when RT variants of > these locks was introduced. > > Fixes: 342a93247e08 ("locking/spinlock: Provide RT variant header: ") Yes that's would be better. > > Lastly, for reference, when posting fixes for Networking code, please: > > * Target the patches at net like this: > > [PATCH net] ... Thanks to let me know for this. > > * Allow at least 24h to pass before posting updated patch versions > > More can be found here: https://docs.kernel.org/process/maintainer-netdev.html > > > Reviewed-by: Simon Horman Thanks for review :). In next patch, I'll reformat the title, change the fix tag and includes your R-b tag. -- Sincerely, Yeoreum Yun