Messages in this thread | | | Date | Mon, 22 Mar 2021 15:49:35 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH next v1 1/3] printk: track/limit recursion |
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On Wed 2021-03-17 00:33:24, John Ogness wrote: > Track printk() recursion and limit it to 3 levels per-CPU and per-context.
Please, explain why it is added. I mean that it will allow remove printk_safe that provides recursion protection at the moment.
> Signed-off-by: John Ogness <john.ogness@linutronix.de> > --- > kernel/printk/printk.c | 80 ++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 77 insertions(+), 3 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 2f829fbf0a13..c666e3e43f0c 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -1940,6 +1940,71 @@ static void call_console_drivers(const char *ext_text, size_t ext_len, > } > } > > +/* > + * Recursion is tracked separately on each CPU. If NMIs are supported, an > + * additional NMI context per CPU is also separately tracked. Until per-CPU > + * is available, a separate "early tracking" is performed. > + */ > +#ifdef CONFIG_PRINTK_NMI
CONFIG_PRINTK_NMI is a shortcut for CONFIG_PRINTK && CONFIG_HAVE_NMI. It should be possible to use CONFIG_HAVE_NMI here because this should be in section where CONFIG_PRINTK is defined.
This would make sense if it allows to remove CONFIG_PRINTK_NMI entirely. IMHO, it would be nice to remove one layer in the config options of possible.
> +#define PRINTK_CTX_NUM 2 > +#else > +#define PRINTK_CTX_NUM 1 > +#endif > +static DEFINE_PER_CPU(char [PRINTK_CTX_NUM], printk_count); > +static char printk_count_early[PRINTK_CTX_NUM]; > + > +/* > + * Recursion is limited to keep the output sane. printk() should not require > + * more than 1 level of recursion (allowing, for example, printk() to trigger > + * a WARN), but a higher value is used in case some printk-internal errors > + * exist, such as the ringbuffer validation checks failing. > + */ > +#define PRINTK_MAX_RECURSION 3 > + > +/* Return a pointer to the dedicated counter for the CPU+context of the caller. */ > +static char *printk_recursion_counter(void) > +{ > + int ctx = 0; > + > +#ifdef CONFIG_PRINTK_NMI > + if (in_nmi()) > + ctx = 1; > +#endif > + if (!printk_percpu_data_ready()) > + return &printk_count_early[ctx]; > + return &((*this_cpu_ptr(&printk_count))[ctx]); > +}
It is not a big deal. But using an array for two contexts looks strange especially when only one is used on some architectures. Also &((*this_cpu_ptr(&printk_count))[ctx]) is quite tricky ;-)
What do you think about the following, please?
static DEFINE_PER_CPU(u8 printk_count); static u8 printk_count_early;
#ifdef CONFIG_HAVE_NMI static DEFINE_PER_CPU(u8 printk_count_nmi); static u8 printk_count_nmi_early; #endif
static u8 *printk_recursion_counter(void) { if (IS_ENABLED(CONFIG_HAVE_NMI) && in_nmi()) { if (printk_cpu_data_ready()) return this_cpu_ptr(&printk_count_nmi); return printk_count_nmi_early; }
if (printk_cpu_data_ready()) return this_cpu_ptr(&printk_count); return printk_count_early; }
Otherwise, it looks good to me. I like the simplicity.
Best Regards, Petr
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