Hi Michael, On Thu, Feb 07, 2019 at 11:46:29PM +1100, Michael Ellerman wrote: > Arch code can set a "dump stack arch description string" which is > displayed with oops output to describe the hardware platform. > > It is useful to initialise this as early as possible, so that an early > oops will have the hardware description. > > However in practice we discover the hardware platform in stages, so it > would be useful to be able to incrementally fill in the hardware > description as we discover it. > > This patch adds that ability, by creating dump_stack_add_arch_desc(). > > If there is no existing string it behaves exactly like > dump_stack_set_arch_desc(). However if there is an existing string it > appends to it, with a leading space. > > This makes it easy to call it multiple times from different parts of the > code and get a reasonable looking result. > > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > --- > include/linux/printk.h | 5 ++++ > lib/dump_stack.c | 58 ++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 63 insertions(+) > > v3: No change, just widened Cc list. > > v2: Add a smp_wmb() and comment. > > v1 is here for reference https://lore.kernel.org/lkml/1430824337-15339-1-git-send-email-mpe@xxxxxxxxxxxxxx/ > > I'll take this series via the powerpc tree if no one minds? > > > diff --git a/include/linux/printk.h b/include/linux/printk.h > index 77740a506ebb..d5fb4f960271 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -198,6 +198,7 @@ u32 log_buf_len_get(void); > void log_buf_vmcoreinfo_setup(void); > void __init setup_log_buf(int early); > __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...); > +__printf(1, 2) void dump_stack_add_arch_desc(const char *fmt, ...); > void dump_stack_print_info(const char *log_lvl); > void show_regs_print_info(const char *log_lvl); > extern asmlinkage void dump_stack(void) __cold; > @@ -256,6 +257,10 @@ static inline __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...) > { > } > > +static inline __printf(1, 2) void dump_stack_add_arch_desc(const char *fmt, ...) > +{ > +} > + > static inline void dump_stack_print_info(const char *log_lvl) > { > } > diff --git a/lib/dump_stack.c b/lib/dump_stack.c > index 5cff72f18c4a..69b710ff92b5 100644 > --- a/lib/dump_stack.c > +++ b/lib/dump_stack.c > @@ -35,6 +35,64 @@ void __init dump_stack_set_arch_desc(const char *fmt, ...) > va_end(args); > } > > +/** > + * dump_stack_add_arch_desc - add arch-specific info to show with task dumps > + * @fmt: printf-style format string > + * @...: arguments for the format string > + * > + * See dump_stack_set_arch_desc() for why you'd want to use this. > + * > + * This version adds to any existing string already created with either > + * dump_stack_set_arch_desc() or dump_stack_add_arch_desc(). If there is an > + * existing string a space will be prepended to the passed string. > + */ > +void __init dump_stack_add_arch_desc(const char *fmt, ...) > +{ > + va_list args; > + int pos, len; > + char *p; > + > + /* > + * If there's an existing string we snprintf() past the end of it, and > + * then turn the terminating NULL of the existing string into a space > + * to create one string separated by a space. > + * > + * If there's no existing string we just snprintf() to the buffer, like > + * dump_stack_set_arch_desc(), but without calling it because we'd need > + * a varargs version. > + */ > + len = strnlen(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str)); > + pos = len; > + > + if (len) > + pos++; > + > + if (pos >= sizeof(dump_stack_arch_desc_str)) > + return; /* Ran out of space */ > + > + p = &dump_stack_arch_desc_str[pos]; > + > + va_start(args, fmt); > + vsnprintf(p, sizeof(dump_stack_arch_desc_str) - pos, fmt, args); > + va_end(args); > + > + if (len) { > + /* > + * Order the stores above in vsnprintf() vs the store of the > + * space below which joins the two strings. Note this doesn't > + * make the code truly race free because there is no barrier on > + * the read side. ie. Another CPU might load the uninitialised > + * tail of the buffer first and then the space below (rather > + * than the NULL that was there previously), and so print the > + * uninitialised tail. But the whole string lives in BSS so in > + * practice it should just see NULLs. The comment doesn't say _why_ we need to order these stores: IOW, what will or can go wrong without this order? This isn't clear to me. Another good practice when adding smp_*-constructs (as discussed, e.g., at KS'18) is to indicate the matching construct/synch. mechanism. Andrea > + */ > + smp_wmb(); > + > + dump_stack_arch_desc_str[len] = ' '; > + } > +} > + > /** > * dump_stack_print_info - print generic debug info for dump_stack() > * @log_lvl: log level > -- > 2.20.1 >
