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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id r2sm31671751wma.1.2019.10.07.06.55.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Oct 2019 06:55:01 -0700 (PDT) Date: Mon, 7 Oct 2019 14:54:59 +0100 From: Daniel Thompson To: Douglas Anderson Cc: Catalin Marinas , Will Deacon , Jason Wessel , kgdb-bugreport@lists.sourceforge.net, Christophe Leroy , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/4] kdb: Fix "btc " crash if the CPU didn't round up Message-ID: <20191007135459.lj3qc2tqzcv3xcia@holly.lan> References: <20190925200220.157670-1-dianders@chromium.org> <20190925125811.v3.3.Id33c06cbd1516b49820faccd80da01c7c4bf15c7@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190925125811.v3.3.Id33c06cbd1516b49820faccd80da01c7c4bf15c7@changeid> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 25, 2019 at 01:02:19PM -0700, Douglas Anderson wrote: > > I noticed that when I did "btc " and the CPU I passed in hadn't > rounded up that I'd crash. I was going to copy the same fix from > commit 162bc7f5afd7 ("kdb: Don't back trace on a cpu that didn't round > up") into the "not all the CPUs" case, but decided it'd be better to > clean things up a little bit. > > This consolidates the two code paths. It is _slightly_ wasteful in in > that the checks for "cpu" being too small or being offline isn't > really needed when we're iterating over all online CPUs, but that > really shouldn't hurt. Better to have the same code path. > > While at it, eliminate at least one slightly ugly (and totally > needless) recursive use of kdb_parse(). > > Signed-off-by: Douglas Anderson > --- > > Changes in v3: > - Patch ("kdb: Fix "btc " crash if the CPU...") new for v3. > > Changes in v2: None > > kernel/debug/kdb/kdb_bt.c | 61 ++++++++++++++++++++++----------------- > 1 file changed, 34 insertions(+), 27 deletions(-) > > diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c > index 120fc686c919..d9af139f9a31 100644 > --- a/kernel/debug/kdb/kdb_bt.c > +++ b/kernel/debug/kdb/kdb_bt.c > @@ -101,6 +101,27 @@ kdb_bt1(struct task_struct *p, unsigned long mask, bool btaprompt) > return 0; > } > > +static void > +kdb_bt_cpu(unsigned long cpu) > +{ > + struct task_struct *kdb_tsk; > + > + if (cpu >= num_possible_cpus() || !cpu_online(cpu)) { > + kdb_printf("WARNING: no process for cpu %ld\n", cpu); > + return; > + } > + > + /* If a CPU failed to round up we could be here */ > + kdb_tsk = KDB_TSK(cpu); > + if (!kdb_tsk) { > + kdb_printf("WARNING: no task for cpu %ld\n", cpu); > + return; > + } > + > + kdb_set_current_task(kdb_tsk); > + kdb_bt1(kdb_tsk, ~0UL, false); > +} > + > int > kdb_bt(int argc, const char **argv) > { > @@ -161,7 +182,6 @@ kdb_bt(int argc, const char **argv) > } else if (strcmp(argv[0], "btc") == 0) { > unsigned long cpu = ~0; > struct task_struct *save_current_task = kdb_current_task; > - char buf[80]; > if (argc > 1) > return KDB_ARGCOUNT; > if (argc == 1) { > @@ -169,35 +189,22 @@ kdb_bt(int argc, const char **argv) > if (diag) > return diag; > } > - /* Recursive use of kdb_parse, do not use argv after > - * this point */ > - argv = NULL; > if (cpu != ~0) { > - if (cpu >= num_possible_cpus() || !cpu_online(cpu)) { > - kdb_printf("no process for cpu %ld\n", cpu); > - return 0; > - } > - sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu)); > - kdb_parse(buf); > - return 0; > - } > - kdb_printf("btc: cpu status: "); > - kdb_parse("cpu\n"); > - for_each_online_cpu(cpu) { > - void *kdb_tsk = KDB_TSK(cpu); > - > - /* If a CPU failed to round up we could be here */ > - if (!kdb_tsk) { > - kdb_printf("WARNING: no task for cpu %ld\n", > - cpu); > - continue; > + kdb_bt_cpu(cpu); > + } else { > + /* > + * Recursive use of kdb_parse, do not use argv after > + * this point. > + */ > + argv = NULL; > + kdb_printf("btc: cpu status: "); > + kdb_parse("cpu\n"); > + for_each_online_cpu(cpu) { > + kdb_bt_cpu(cpu); > + touch_nmi_watchdog(); > } > - > - sprintf(buf, "btt 0x%px\n", kdb_tsk); > - kdb_parse(buf); > - touch_nmi_watchdog(); > + kdb_set_current_task(save_current_task); > } > - kdb_set_current_task(save_current_task); Why does this move out into only one of the conditional branches? Don't both of the above paths modify the current task? Daniel. > return 0; > } else { > if (argc) { > -- > 2.23.0.351.gc4317032e6-goog >