From: Markus Stockhausen Date: Wed, 23 Jul 2025 05:37:02 +0000 (-0400) Subject: realtek: don't disable MIPS counter on secondary VPEs X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=21d3722c4072e1888c2beea2ee7c058376193d5f;p=thirdparty%2Fopenwrt.git realtek: don't disable MIPS counter on secondary VPEs After observation that timer interrupt 7 always fires on secondary VPEs the counter was disabled in the startup code. This is a bad idea when building the kernel with jitterentropy. To generate entropy it makes use of function random_get_entropy(). On MIPS architecture this simply reads the counter register on the current core. With a disabled counter it always returns the same value and the entropy initialization stalls the core if it runs on a secondary VPE. See backtrace [ 21.736246] rcu: INFO: rcu_sched self-detected stall on CPU [ 21.736246] rcu: INFO: rcu_sched self-detected stall on CPU [ 21.748594] rcu: 1-....: (2100 ticks this GP) idle=064c/1/0x40000002 softirq=7/7 fqs=1050 [ 21.748594] rcu: 1-....: (2100 ticks this GP) idle=064c/1/0x40000002 softirq=7/7 fqs=1050 [ 21.766871] rcu: (t=2102 jiffies g=-1187 q=25 ncpus=2) [ 21.766871] rcu: (t=2102 jiffies g=-1187 q=25 ncpus=2) [ 21.778429] CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.39 #482 [ 21.778429] CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.39 #482 [ 21.778461] Hardware name: Zyxel GS1900-48 [ 21.778461] Hardware name: Zyxel GS1900-48 ... [ 21.779757] [<8029b968>] jent_measure_jitter+0xc8/0x10c [ 21.779757] [<8029b968>] jent_measure_jitter+0xc8/0x10c [ 21.779779] [<8029b9e8>] jent_gen_entropy+0x3c/0xb0 [ 21.779779] [<8029b9e8>] jent_gen_entropy+0x3c/0xb0 [ 21.779800] [<8029bcc0>] jent_entropy_collector_alloc+0x104/0x118 [ 21.779800] [<8029bcc0>] jent_entropy_collector_alloc+0x104/0x118 [ 21.779822] [<8029bd6c>] jent_entropy_init+0x4c/0x2ec [ 21.779822] [<8029bd6c>] jent_entropy_init+0x4c/0x2ec [ 21.779844] [<8086f184>] jent_mod_init+0x58/0xac [ 21.779844] [<8086f184>] jent_mod_init+0x58/0xac [ 21.779865] [<80100200>] do_one_initcall+0x70/0x250 [ 21.779865] [<80100200>] do_one_initcall+0x70/0x250 [ 21.779883] [<8085c018>] kernel_init_freeable+0x1f0/0x280 [ 21.779883] [<8085c018>] kernel_init_freeable+0x1f0/0x280 [ 21.779905] [<8067cba4>] kernel_init+0x20/0xb0 [ 21.779905] [<8067cba4>] kernel_init+0x20/0xb0 [ 21.779926] [<80101158>] ret_from_kernel_thread+0x14/0x1c [ 21.779926] [<80101158>] ret_from_kernel_thread+0x14/0x1c This bit of entropy is helpful on these low end devices. Reenable the counter and simply disable the interrupt. Fixes: b7aab1958591e6290 ("realtek: SMP handling of R4K timer interrupts") Reported-by: Sebastian Gottschall Signed-off-by: Markus Stockhausen Link: https://github.com/openwrt/openwrt/pull/19499 Signed-off-by: Hauke Mehrtens --- diff --git a/target/linux/realtek/files-6.12/arch/mips/rtl838x/prom.c b/target/linux/realtek/files-6.12/arch/mips/rtl838x/prom.c index c2c4b09d1d1..68b4e5c1449 100644 --- a/target/linux/realtek/files-6.12/arch/mips/rtl838x/prom.c +++ b/target/linux/realtek/files-6.12/arch/mips/rtl838x/prom.c @@ -13,6 +13,7 @@ #include #include #include +#include #include @@ -41,13 +42,13 @@ static void rtlsmp_finish(void) { /* These devices are low on resources. There might be the chance that CEVT_R4K is * not enabled in kernel build. Nevertheless the timer and interrupt 7 might be - * active by default after startup of secondary VPE. With no registered handler - * that leads to continuous unhandeled interrupts. In this case disable counting - * (DC) in the core and confirm a pending interrupt. + * active by default after startup of secondary VPEs. With no registered handler + * that leads to continuous unhandeled interrupts. Disable it but keep the counter + * running so it can still be used as an entropy source. */ if (!IS_ENABLED(CONFIG_CEVT_R4K)) { - write_c0_cause(read_c0_cause() | CAUSEF_DC); - write_c0_compare(0); + write_c0_status(read_c0_status() & ~CAUSEF_IP7); + write_c0_compare(read_c0_count() - 1); } local_irq_enable();