| Message ID | 20200513160501.1.I0b5edf030cc6ebef6ab4829f8867cdaea42485d8@changeid (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | b322c65f8ca37396cfd7d4d0ac2f7f2dc08fa9eb |
| Headers | show |
| Series | arm64: Call debug_traps_init() from trap_init() to help early kgdb | expand |
On Wed, May 13, 2020 at 04:06:37PM -0700, Douglas Anderson wrote: > A new kgdb feature will soon land (kgdb_earlycon) that lets us run > kgdb much earlier. In order for everything to work properly it's > important that the break hook is setup by the time we process > "kgdbwait". > > Right now the break hook is setup in debug_traps_init() and that's > called from arch_initcall(). That's a bit too late since > kgdb_earlycon really needs things to be setup by the time the system > calls dbg_late_init(). > > We could fix this by adding call_break_hook() into early_brk64() and > that works fine. However, it's a little ugly. Instead, let's just > add a call to debug_traps_init() straight from trap_init(). There's > already a documented dependency between trap_init() and > debug_traps_init() and this makes the dependency more obvious rather > than just relying on a comment. > > NOTE: this solution isn't early enough to let us select the > "ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the > kgdb_earlycon patch series. That would only be set if we could do > breakpoints when early params are parsed. This patch only enables > "late early" breakpoints, AKA breakpoints when dbg_late_init() is > called. It's expected that this should be fine for most people. > > It should also be noted that if you crash you can still end up in kgdb > earlier than debug_traps_init(). Since you don't need breakpoints to > debug a crash that's fine. > > Suggested-by: Will Deacon <will@kernel.org> > Signed-off-by: Douglas Anderson <dianders@chromium.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > --- > This replaces the patch ("arm64: Add call_break_hook() to > early_brk64() for early kgdb") in my recent kgdb series [1]. If I end > up re-posting that series again I'll include this patch as a > replacement, but I'm sending it separately to avoid spamming a pile of > people another time with a 12-patch series. > > Note that, because it doesn't select the "ARCH_HAS_EARLY_DEBUG" > KConfig option it could be landed standalone. However, it's still > probably better to land together with that patch series. > > If the kgdb_earlycon patch series lands without this patch then > kgdbwait + kgdb_earlycon won't work well on arm64, but there would be > no other bad side effects. > > If this patch lands without the kgdb_earlycon patch series then there > will be no known problems. > > [1] https://lore.kernel.org/r/20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid > > arch/arm64/include/asm/debug-monitors.h | 2 ++ > arch/arm64/kernel/debug-monitors.c | 4 +--- > arch/arm64/kernel/traps.c | 2 +- > 3 files changed, 4 insertions(+), 4 deletions(-) [...] Acked-by: Will Deacon <will@kernel.org> I would prefer to take this via arm64, if possible, since we have quite lot going in for 5.8, although I don't think this conflicts at the moment. Daniel -- what do you want to do? Will
On Fri, May 15, 2020 at 05:23:17PM +0100, Will Deacon wrote: > On Wed, May 13, 2020 at 04:06:37PM -0700, Douglas Anderson wrote: > > A new kgdb feature will soon land (kgdb_earlycon) that lets us run > > kgdb much earlier. In order for everything to work properly it's > > important that the break hook is setup by the time we process > > "kgdbwait". > > > > Right now the break hook is setup in debug_traps_init() and that's > > called from arch_initcall(). That's a bit too late since > > kgdb_earlycon really needs things to be setup by the time the system > > calls dbg_late_init(). > > > > We could fix this by adding call_break_hook() into early_brk64() and > > that works fine. However, it's a little ugly. Instead, let's just > > add a call to debug_traps_init() straight from trap_init(). There's > > already a documented dependency between trap_init() and > > debug_traps_init() and this makes the dependency more obvious rather > > than just relying on a comment. > > > > NOTE: this solution isn't early enough to let us select the > > "ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the > > kgdb_earlycon patch series. That would only be set if we could do > > breakpoints when early params are parsed. This patch only enables > > "late early" breakpoints, AKA breakpoints when dbg_late_init() is > > called. It's expected that this should be fine for most people. > > > > It should also be noted that if you crash you can still end up in kgdb > > earlier than debug_traps_init(). Since you don't need breakpoints to > > debug a crash that's fine. > > > > Suggested-by: Will Deacon <will@kernel.org> > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > Cc: Catalin Marinas <catalin.marinas@arm.com> > > Cc: Will Deacon <will@kernel.org> > > --- > > This replaces the patch ("arm64: Add call_break_hook() to > > early_brk64() for early kgdb") in my recent kgdb series [1]. If I end > > up re-posting that series again I'll include this patch as a > > replacement, but I'm sending it separately to avoid spamming a pile of > > people another time with a 12-patch series. > > > > Note that, because it doesn't select the "ARCH_HAS_EARLY_DEBUG" > > KConfig option it could be landed standalone. However, it's still > > probably better to land together with that patch series. > > > > If the kgdb_earlycon patch series lands without this patch then > > kgdbwait + kgdb_earlycon won't work well on arm64, but there would be > > no other bad side effects. > > > > If this patch lands without the kgdb_earlycon patch series then there > > will be no known problems. > > > > [1] https://lore.kernel.org/r/20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid > > > > arch/arm64/include/asm/debug-monitors.h | 2 ++ > > arch/arm64/kernel/debug-monitors.c | 4 +--- > > arch/arm64/kernel/traps.c | 2 +- > > 3 files changed, 4 insertions(+), 4 deletions(-) > > [...] > > Acked-by: Will Deacon <will@kernel.org> > > I would prefer to take this via arm64, if possible, since we have quite lot > going in for 5.8, although I don't think this conflicts at the moment. > > Daniel -- what do you want to do? I'm very happy for you to take it! On my side I hope to get the rest of the patchset into linux-next early next week. Daniel.
On Wed, 13 May 2020 16:06:37 -0700, Douglas Anderson wrote: > A new kgdb feature will soon land (kgdb_earlycon) that lets us run > kgdb much earlier. In order for everything to work properly it's > important that the break hook is setup by the time we process > "kgdbwait". > > Right now the break hook is setup in debug_traps_init() and that's > called from arch_initcall(). That's a bit too late since > kgdb_earlycon really needs things to be setup by the time the system > calls dbg_late_init(). > > [...] Applied to arm64 (for-next/misc), thanks! [1/1] arm64: Call debug_traps_init() from trap_init() to help early kgdb https://git.kernel.org/arm64/c/b322c65f8ca3 Cheers,
diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index 7619f473155f..e5ceea213e39 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -125,5 +125,7 @@ static inline int reinstall_suspended_bps(struct pt_regs *regs) int aarch32_break_handler(struct pt_regs *regs); +void debug_traps_init(void); + #endif /* __ASSEMBLY */ #endif /* __ASM_DEBUG_MONITORS_H */ diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 48222a4760c2..15e80c876d46 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -376,15 +376,13 @@ int aarch32_break_handler(struct pt_regs *regs) } NOKPROBE_SYMBOL(aarch32_break_handler); -static int __init debug_traps_init(void) +void __init debug_traps_init(void) { hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, TRAP_TRACE, "single-step handler"); hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, TRAP_BRKPT, "ptrace BRK handler"); - return 0; } -arch_initcall(debug_traps_init); /* Re-enable single step for syscall restarting. */ void user_rewind_single_step(struct task_struct *task) diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index cf402be5c573..8408e8670f2e 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -1047,11 +1047,11 @@ int __init early_brk64(unsigned long addr, unsigned int esr, return bug_handler(regs, esr) != DBG_HOOK_HANDLED; } -/* This registration must happen early, before debug_traps_init(). */ void __init trap_init(void) { register_kernel_break_hook(&bug_break_hook); #ifdef CONFIG_KASAN_SW_TAGS register_kernel_break_hook(&kasan_break_hook); #endif + debug_traps_init(); }
A new kgdb feature will soon land (kgdb_earlycon) that lets us run kgdb much earlier. In order for everything to work properly it's important that the break hook is setup by the time we process "kgdbwait". Right now the break hook is setup in debug_traps_init() and that's called from arch_initcall(). That's a bit too late since kgdb_earlycon really needs things to be setup by the time the system calls dbg_late_init(). We could fix this by adding call_break_hook() into early_brk64() and that works fine. However, it's a little ugly. Instead, let's just add a call to debug_traps_init() straight from trap_init(). There's already a documented dependency between trap_init() and debug_traps_init() and this makes the dependency more obvious rather than just relying on a comment. NOTE: this solution isn't early enough to let us select the "ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the kgdb_earlycon patch series. That would only be set if we could do breakpoints when early params are parsed. This patch only enables "late early" breakpoints, AKA breakpoints when dbg_late_init() is called. It's expected that this should be fine for most people. It should also be noted that if you crash you can still end up in kgdb earlier than debug_traps_init(). Since you don't need breakpoints to debug a crash that's fine. Suggested-by: Will Deacon <will@kernel.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> --- This replaces the patch ("arm64: Add call_break_hook() to early_brk64() for early kgdb") in my recent kgdb series [1]. If I end up re-posting that series again I'll include this patch as a replacement, but I'm sending it separately to avoid spamming a pile of people another time with a 12-patch series. Note that, because it doesn't select the "ARCH_HAS_EARLY_DEBUG" KConfig option it could be landed standalone. However, it's still probably better to land together with that patch series. If the kgdb_earlycon patch series lands without this patch then kgdbwait + kgdb_earlycon won't work well on arm64, but there would be no other bad side effects. If this patch lands without the kgdb_earlycon patch series then there will be no known problems. [1] https://lore.kernel.org/r/20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid arch/arm64/include/asm/debug-monitors.h | 2 ++ arch/arm64/kernel/debug-monitors.c | 4 +--- arch/arm64/kernel/traps.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-)