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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id y185sm6151594wmg.34.2018.12.03.08.03.20 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 03 Dec 2018 08:03:20 -0800 (PST) Date: Mon, 3 Dec 2018 16:03:18 +0000 From: Daniel Thompson To: Douglas Anderson Cc: Jason Wessel , Will Deacon , kgdb-bugreport@lists.sourceforge.net, Peter Zijlstra , Christophe Leroy , linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 4/4] kdb: Don't back trace on a cpu that didn't round up Message-ID: <20181203160318.35idsm2vb3licod6@holly.lan> References: <20181127173839.34328-1-dianders@chromium.org> <20181127173839.34328-5-dianders@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181127173839.34328-5-dianders@chromium.org> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 27, 2018 at 09:38:39AM -0800, Douglas Anderson wrote: > If you have a CPU that fails to round up and then run 'btc' you'll end > up crashing in kdb becaue we dereferenced NULL. Let's add a check. > It's wise to also set the task to NULL when leaving the debugger so > that if we fail to round up on a later entry into the debugger we > won't backtrace a stale task. > > Signed-off-by: Douglas Anderson Acked-by: Daniel Thompson > --- > > Changes in v6: None > Changes in v5: None > Changes in v4: > - Also clear out .debuggerinfo. > - Also clear out .debuggerinfo and .task for the master. > - Remove clearing out in kdb_stub for offline CPUs; it's now redundant. > > Changes in v3: > - Don't back trace on a cpu that didn't round up new for v3. > > Changes in v2: None > > kernel/debug/debug_core.c | 4 ++++ > kernel/debug/kdb/kdb_bt.c | 11 ++++++++++- > kernel/debug/kdb/kdb_debugger.c | 7 ------- > 3 files changed, 14 insertions(+), 8 deletions(-) > > diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c > index 1fb8b239e567..5cc608de6883 100644 > --- a/kernel/debug/debug_core.c > +++ b/kernel/debug/debug_core.c > @@ -592,6 +592,8 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs, > arch_kgdb_ops.correct_hw_break(); > if (trace_on) > tracing_on(); > + kgdb_info[cpu].debuggerinfo = NULL; > + kgdb_info[cpu].task = NULL; > kgdb_info[cpu].exception_state &= > ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE); > kgdb_info[cpu].enter_kgdb--; > @@ -724,6 +726,8 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs, > if (trace_on) > tracing_on(); > > + kgdb_info[cpu].debuggerinfo = NULL; > + kgdb_info[cpu].task = NULL; > kgdb_info[cpu].exception_state &= > ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE); > kgdb_info[cpu].enter_kgdb--; > diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c > index 7921ae4fca8d..7e2379aa0a1e 100644 > --- a/kernel/debug/kdb/kdb_bt.c > +++ b/kernel/debug/kdb/kdb_bt.c > @@ -186,7 +186,16 @@ kdb_bt(int argc, const char **argv) > kdb_printf("btc: cpu status: "); > kdb_parse("cpu\n"); > for_each_online_cpu(cpu) { > - sprintf(buf, "btt 0x%px\n", KDB_TSK(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; > + } > + > + sprintf(buf, "btt 0x%px\n", kdb_tsk); > kdb_parse(buf); > touch_nmi_watchdog(); > } > diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c > index 15e1a7af5dd0..53a0df6e4d92 100644 > --- a/kernel/debug/kdb/kdb_debugger.c > +++ b/kernel/debug/kdb/kdb_debugger.c > @@ -118,13 +118,6 @@ int kdb_stub(struct kgdb_state *ks) > kdb_bp_remove(); > KDB_STATE_CLEAR(DOING_SS); > KDB_STATE_SET(PAGER); > - /* zero out any offline cpu data */ > - for_each_present_cpu(i) { > - if (!cpu_online(i)) { > - kgdb_info[i].debuggerinfo = NULL; > - kgdb_info[i].task = NULL; > - } > - } > if (ks->err_code == DIE_OOPS || reason == KDB_REASON_OOPS) { > ks->pass_exception = 1; > KDB_FLAG_SET(CATASTROPHIC); > -- > 2.20.0.rc0.387.gc7a69e6b6c-goog >