From 32f6bd51ece0b25a9c01ba6b5374f538beab5dd9 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Wed, 28 Sep 2011 10:50:37 +1000 Subject: [PATCH] dynamic_debug: use a single printk() to emit messages We were using KERN_CONT to combine messages with their prefix. However, KERN_CONT is not smp safe, in the sense that it can interleave messages. This interleaving can result in printks coming out at the wrong loglevel. With the high frequency of printks that dynamic debug can produce this is not desirable. So make dynamic_emit_prefix() fill a char buf[64] instead of doing a printk directly. If we enable printing out of function, module, line, or pid info, they are placed in this 64 byte buffer. In my testing 64 bytes was enough size to fulfill all requests. Even if it's not, we can match up the printk itself to see where it's from, so to me this is no big deal. [akpm@linux-foundation.org: convert dangerous macro to C] Signed-off-by: Jason Baron Cc: Greg KH Cc: Arnd Bergmann Signed-off-by: Andrew Morton <> --- lib/dynamic_debug.c | 80 +++++++++++++++++++++++---------------------- 1 file changed, 41 insertions(+), 39 deletions(-) diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c index 6a07c2a9c0af..9a374abb5252 100644 --- a/lib/dynamic_debug.c +++ b/lib/dynamic_debug.c @@ -421,52 +421,60 @@ static int ddebug_exec_query(char *query_string) return 0; } -static int dynamic_emit_prefix(const struct _ddebug *descriptor) +#define PREFIX_SIZE 64 + +static int remaining(int wrote) +{ + if (PREFIX_SIZE - wrote > 0) + return PREFIX_SIZE - wrote; + return 0; +} + +static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf) { - char tid[sizeof(int) + sizeof(int)/2 + 4]; - char lineno[sizeof(int) + sizeof(int)/2]; + int pos_after_tid; + int pos = 0; - if (descriptor->flags & _DPRINTK_FLAGS_INCL_TID) { + pos += snprintf(buf + pos, remaining(pos), "%s", KERN_DEBUG); + if (desc->flags & _DPRINTK_FLAGS_INCL_TID) { if (in_interrupt()) - snprintf(tid, sizeof(tid), "%s", " "); + pos += snprintf(buf + pos, remaining(pos), "%s ", + ""); else - snprintf(tid, sizeof(tid), "[%d] ", - task_pid_vnr(current)); - } else { - tid[0] = 0; + pos += snprintf(buf + pos, remaining(pos), "[%d] ", + task_pid_vnr(current)); } + pos_after_tid = pos; + if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME) + pos += snprintf(buf + pos, remaining(pos), "%s:", + desc->modname); + if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME) + pos += snprintf(buf + pos, remaining(pos), "%s:", + desc->function); + if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO) + pos += snprintf(buf + pos, remaining(pos), "%d:", desc->lineno); + if (pos - pos_after_tid) + pos += snprintf(buf + pos, remaining(pos), " "); + if (pos >= PREFIX_SIZE) + buf[PREFIX_SIZE - 1] = '\0'; - if (descriptor->flags & _DPRINTK_FLAGS_INCL_LINENO) - snprintf(lineno, sizeof(lineno), "%d", descriptor->lineno); - else - lineno[0] = 0; - - return printk(KERN_DEBUG "%s%s%s%s%s%s", - tid, - (descriptor->flags & _DPRINTK_FLAGS_INCL_MODNAME) ? - descriptor->modname : "", - (descriptor->flags & _DPRINTK_FLAGS_INCL_MODNAME) ? - ":" : "", - (descriptor->flags & _DPRINTK_FLAGS_INCL_FUNCNAME) ? - descriptor->function : "", - (descriptor->flags & _DPRINTK_FLAGS_INCL_FUNCNAME) ? - ":" : "", - lineno); + return buf; } int __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...) { va_list args; int res; + struct va_format vaf; + char buf[PREFIX_SIZE]; BUG_ON(!descriptor); BUG_ON(!fmt); va_start(args, fmt); - - res = dynamic_emit_prefix(descriptor); - res += vprintk(fmt, args); - + vaf.fmt = fmt; + vaf.va = &args; + res = printk("%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf); va_end(args); return res; @@ -479,18 +487,15 @@ int __dynamic_dev_dbg(struct _ddebug *descriptor, struct va_format vaf; va_list args; int res; + char buf[PREFIX_SIZE]; BUG_ON(!descriptor); BUG_ON(!fmt); va_start(args, fmt); - vaf.fmt = fmt; vaf.va = &args; - - res = dynamic_emit_prefix(descriptor); - res += __dev_printk(KERN_CONT, dev, &vaf); - + res = __dev_printk(dynamic_emit_prefix(descriptor, buf), dev, &vaf); va_end(args); return res; @@ -503,18 +508,15 @@ int __dynamic_netdev_dbg(struct _ddebug *descriptor, struct va_format vaf; va_list args; int res; + char buf[PREFIX_SIZE]; BUG_ON(!descriptor); BUG_ON(!fmt); va_start(args, fmt); - vaf.fmt = fmt; vaf.va = &args; - - res = dynamic_emit_prefix(descriptor); - res += __netdev_printk(KERN_CONT, dev, &vaf); - + res = __netdev_printk(dynamic_emit_prefix(descriptor, buf), dev, &vaf); va_end(args); return res; -- 2.39.5