# git rev-parse -q --verify 7c6986ade69e3c81bac831645bc72109cd798a80^{commit} 7c6986ade69e3c81bac831645bc72109cd798a80 already have revision, skipping fetch # git checkout -q -f -B kisskb 7c6986ade69e3c81bac831645bc72109cd798a80 # git clean -qxdf # < git log -1 # commit 7c6986ade69e3c81bac831645bc72109cd798a80 # Author: Michael Ellerman # Date: Fri Jun 25 16:28:41 2021 +1000 # # powerpc/stacktrace: Fix spurious "stale" traces in raise_backtrace_ipi() # # In raise_backtrace_ipi() we iterate through the cpumask of CPUs, sending # each an IPI asking them to do a backtrace, but we don't wait for the # backtrace to happen. # # We then iterate through the CPU mask again, and if any CPU hasn't done # the backtrace and cleared itself from the mask, we print a trace on its # behalf, noting that the trace may be "stale". # # This works well enough when a CPU is not responding, because in that # case it doesn't receive the IPI and the sending CPU is left to print the # trace. But when all CPUs are responding we are left with a race between # the sending and receiving CPUs, if the sending CPU wins the race then it # will erroneously print a trace. # # This leads to spurious "stale" traces from the sending CPU, which can # then be interleaved messily with the receiving CPU, note the CPU # numbers, eg: # # [ 1658.929157][ C7] rcu: Stack dump where RCU GP kthread last ran: # [ 1658.929223][ C7] Sending NMI from CPU 7 to CPUs 1: # [ 1658.929303][ C1] NMI backtrace for cpu 1 # [ 1658.929303][ C7] CPU 1 didn't respond to backtrace IPI, inspecting paca. # [ 1658.929362][ C1] CPU: 1 PID: 325 Comm: kworker/1:1H Tainted: G W E 5.13.0-rc2+ #46 # [ 1658.929405][ C7] irq_soft_mask: 0x01 in_mce: 0 in_nmi: 0 current: 325 (kworker/1:1H) # [ 1658.929465][ C1] Workqueue: events_highpri test_work_fn [test_lockup] # [ 1658.929549][ C7] Back trace of paca->saved_r1 (0xc0000000057fb400) (possibly stale): # [ 1658.929592][ C1] NIP: c00000000002cf50 LR: c008000000820178 CTR: c00000000002cfa0 # # To fix it, change the logic so that the sending CPU waits 5s for the # receiving CPU to print its trace. If the receiving CPU prints its trace # successfully then the sending CPU just continues, avoiding any spurious # "stale" trace. # # This has the added benefit of allowing all CPUs to print their traces in # order and avoids any interleaving of their output. # # Fixes: 5cc05910f26e ("powerpc/64s: Wire up arch_trigger_cpumask_backtrace()") # Cc: stable@vger.kernel.org # v4.18+ # Reported-by: Nathan Lynch # Signed-off-by: Michael Ellerman # Link: https://lore.kernel.org/r/20210625140408.3351173-1-mpe@ellerman.id.au # < /opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux-gcc --version # < /opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux-ld --version # < git log --format=%s --max-count=1 7c6986ade69e3c81bac831645bc72109cd798a80 # < make -s -j 48 ARCH=mips O=/kisskb/build/powerpc-next_mips-defconfig_mipsel CROSS_COMPILE=/opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux- defconfig # < make -s -j 48 ARCH=mips O=/kisskb/build/powerpc-next_mips-defconfig_mipsel CROSS_COMPILE=/opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux- help # make -s -j 48 ARCH=mips O=/kisskb/build/powerpc-next_mips-defconfig_mipsel CROSS_COMPILE=/opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux- olddefconfig # make -s -j 48 ARCH=mips O=/kisskb/build/powerpc-next_mips-defconfig_mipsel CROSS_COMPILE=/opt/cross/kisskb/br-mipsel-o32-full-2016.08-613-ge98b4dd/bin/mipsel-linux- FIT description: Linux 5.13.0-rc2-g7c6986ade69e Created: Sun Jul 18 12:44:14 2021 Image 0 (kernel) Description: Linux 5.13.0-rc2-g7c6986ade69e Created: Sun Jul 18 12:44:14 2021 Type: Kernel Image Compression: gzip compressed Data Size: 5350427 Bytes = 5225.03 KiB = 5.10 MiB Architecture: MIPS OS: Linux Load Address: 0x80100000 Entry Point: 0x809d0ab8 Hash algo: sha1 Hash value: 19161be558e1d0f35cc331438b42bc9d438a73aa Image 1 (fdt-boston) Description: img,boston Device Tree Created: Sun Jul 18 12:44:14 2021 Type: Flat Device Tree Compression: uncompressed Data Size: 3793 Bytes = 3.70 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 4799f50d688573234da6e9d7701234d394759ef4 Image 2 (fdt-ni169445) Description: NI 169445 device tree Created: Sun Jul 18 12:44:14 2021 Type: Flat Device Tree Compression: uncompressed Data Size: 1871 Bytes = 1.83 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 51b89b31605ee62038c8468c429af091dfc75ec7 Image 3 (fdt-ocelot_pcb123) Description: MSCC Ocelot PCB123 Device Tree Created: Sun Jul 18 12:44:14 2021 Type: Flat Device Tree Compression: uncompressed Data Size: 4659 Bytes = 4.55 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 5bcb6e4f21e8e5372544aa130b3bd097355a9050 Image 4 (fdt-ocelot_pcb120) Description: MSCC Ocelot PCB120 Device Tree Created: Sun Jul 18 12:44:14 2021 Type: Flat Device Tree Compression: uncompressed Data Size: 5418 Bytes = 5.29 KiB = 0.01 MiB Architecture: MIPS Hash algo: sha1 Hash value: 93d882f2009a217e0fa9dab94788535ed2be8476 Image 5 (fdt-xilfpga) Description: MIPSfpga (xilfpga) Device Tree Created: Sun Jul 18 12:44:14 2021 Type: Flat Device Tree Compression: uncompressed Data Size: 2708 Bytes = 2.64 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 63d058b780f65e22da30f0a183433765f1807f1d Default Configuration: 'conf-default' Configuration 0 (conf-default) Description: Generic Linux kernel Kernel: kernel Configuration 1 (conf-boston) Description: Boston Linux kernel Kernel: kernel FDT: fdt-boston Configuration 2 (conf-ni169445) Description: NI 169445 Linux Kernel Kernel: kernel FDT: fdt-ni169445 Configuration 3 (conf-ocelot_pcb123) Description: Ocelot Linux kernel Kernel: kernel FDT: fdt-ocelot_pcb123 Configuration 4 (conf-ocelot_pcb120) Description: Ocelot Linux kernel Kernel: kernel FDT: fdt-ocelot_pcb120 Configuration 5 (conf-xilfpga) Description: MIPSfpga Linux kernel Kernel: kernel FDT: fdt-xilfpga Completed OK # rm -rf /kisskb/build/powerpc-next_mips-defconfig_mipsel # Build took: 0:01:38.360677