Messages in this thread | | | Date | Fri, 7 Jul 2023 11:02:10 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected |
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On Thu, 6 Jul 2023 09:50:39 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Thu, 6 Jul 2023 13:40:36 +0900 > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > > On Wed, 5 Jul 2023 22:49:56 -0400 > > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > On Sun, 2 Jul 2023 23:47:35 +0900 > > > "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote: > > > > > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > > > > > > > When the "(fault)" is injected, the return value of fetch_store_string*() > > > > should be the length of the "(fault)", but an error code is returned. > > > > Fix it to return the correct length and update the data_loc according the > > > > updated length. > > > > This needs to update a ftracetest test case, which expects trace output > > > > to appear as '(fault)' instead of '"(fault)"'. > > > > > > > > > > Ah, because of patch 2, the ret < 0 makes it return without printing the > > > "fault"? > > > > No, actually set_data_loc() updates the 'ret' argument, but it is just > > disposed... (not returned to the caller) > > That's not what I was talking about. > > We have: > > process_fetch_insn_bottom() { > [..] > case FETCH_OP_ST_STRING: > loc = *(u32 *)dest; > ret = fetch_store_string(val + code->offset, dest, base); > break; > [..] > > // And from patch 2 we have: > > @@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val, > default: > return -EILSEQ; > } > + if (ret < 0) > + return ret; > code++; > > And now that the return value of fetch_store_string() is being checked, and > if it returns negative, it ends the function before being processed > further. And if there's a fault, it happens to return negative! > > This patch now changes fetch_store_string() and fetch_store_string_user() > to not return negative if there's a fault. As this patch has: > > @@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base) > * probing. > */ > ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen); > - set_data_loc(ret, dest, __dest, base, maxlen); > - > - return ret; > + return set_data_loc(ret, dest, __dest, base, maxlen); > } > > But to do that, you needed to update set_data_loc() to return a value. > > *that's* what I meant by > > 'Ah, because of patch 2, the ret < 0 makes it return without printing the "fault"?'
Yes, that's correct. Actually, the data ("(fault)") is stored, but ignored because data_loc is not updated.
But wait, it seems that the print function shows (fault), so commit 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes") may not needed?
---- /* Print type function for string type */ int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent) { int len = *(u32 *)data >> 16;
if (!len) trace_seq_puts(s, "(fault)"); else ----
In this case, what we need is to set data_loc length = 0 if ret < 0.
Do you really need to get '"(fault)"' (with double quotation) or just '(fault)' (no double quotation) is OK?
Thank you, > > > -- Steve > > > > > -static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len) > > +static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len) > > { > > - if (ret >= 0) { > > - *(u32 *)dest = make_data_loc(ret, __dest - base); > > - } else { > > + if (ret < 0) { > > strscpy(__dest, FAULT_STRING, len); > > ret = strlen(__dest) + 1; > > } > > + > > + *(u32 *)dest = make_data_loc(ret, __dest - base); > > + return ret; > > } > > > > So this returns updated 'ret', and also update data_loc to use the > > updated 'ret' value (which is the length of the stored data). > > > > > > > > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> > > > > Thank you! > > > > > > > > -- Steve > > > > > > > > > > Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes") > > > > Cc: stable@vger.kernel.org > > > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > > > --- > > > > >
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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