From: Mahesh Salgaonkar Date: Mon, 24 Oct 2016 18:21:51 +0000 (+0530) Subject: powerpc/fadump: Fix the race in crash_fadump(). X-Git-Tag: v4.11-rc1~122^2~86 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=f2a5e8f0023eba847ad2adb145b2f631934bb12b;p=linux.git powerpc/fadump: Fix the race in crash_fadump(). There are chances that multiple CPUs can call crash_fadump() simultaneously and would start duplicating same info to vmcoreinfo ELF note section. This causes makedumpfile to fail during kdump capture. One example is, triggering dumprestart from HMC which sends system reset to all the CPUs at once. makedumpfile --dump-dmesg /proc/vmcore read_vmcoreinfo_basic_info: Invalid data in /tmp/vmcoreinfoyjgxlL: CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971 makedumpfile Failed. Running makedumpfile --dump-dmesg /proc/vmcore failed (1). makedumpfile -d 31 -l /proc/vmcore read_vmcoreinfo_basic_info: Invalid data in /tmp/vmcoreinfo1mmVdO: CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971CRASHTIME=1475605971 makedumpfile Failed. Running makedumpfile -d 31 -l /proc/vmcore failed (1). Signed-off-by: Mahesh Salgaonkar Signed-off-by: Michael Ellerman --- diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c index 8f0c7c5d93f2..8ff0dd4e77a7 100644 --- a/arch/powerpc/kernel/fadump.c +++ b/arch/powerpc/kernel/fadump.c @@ -406,12 +406,35 @@ static void register_fw_dump(struct fadump_mem_struct *fdm) void crash_fadump(struct pt_regs *regs, const char *str) { struct fadump_crash_info_header *fdh = NULL; + int old_cpu, this_cpu; if (!fw_dump.dump_registered || !fw_dump.fadumphdr_addr) return; + /* + * old_cpu == -1 means this is the first CPU which has come here, + * go ahead and trigger fadump. + * + * old_cpu != -1 means some other CPU has already on it's way + * to trigger fadump, just keep looping here. + */ + this_cpu = smp_processor_id(); + old_cpu = cmpxchg(&crashing_cpu, -1, this_cpu); + + if (old_cpu != -1) { + /* + * We can't loop here indefinitely. Wait as long as fadump + * is in force. If we race with fadump un-registration this + * loop will break and then we go down to normal panic path + * and reboot. If fadump is in force the first crashing + * cpu will definitely trigger fadump. + */ + while (fw_dump.dump_registered) + cpu_relax(); + return; + } + fdh = __va(fw_dump.fadumphdr_addr); - crashing_cpu = smp_processor_id(); fdh->crashing_cpu = crashing_cpu; crash_save_vmcoreinfo();