From f2d28a2ebcb525a6ec7e2152106ddb385ef52b73 Mon Sep 17 00:00:00 2001 From: Guillaume Knispel Date: Tue, 17 Mar 2009 16:18:42 +0100 Subject: printk: correct the behavior of printk_timed_ratelimit() Impact: fix jiffies-comparison sign-wrap behavior The behavior provided by printk_timed_ratelimit() is, in some situations, probably not what a caller would reasonably expect: bool printk_timed_ratelimit(unsigned long *caller_jiffies, unsigned int interval_msecs) { if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) { *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs); return true; } return false; } On a 32 bit computer, if printk_timed_ratelimit() is initially called at time jiffies == Ja, *caller_jiffies is set to Ja + msecs_to_jiffies(interval_msecs): let's say Ja + 42 for this example. If this caller then doesn't call printk_timed_ratelimit() until jiffies == Ja + (1 << 31) + 42 (which can happen as soon as ~ 25 days later on a 1000 HZ system), printk_timed_ratelimit() will then always return false to this caller until jiffies loops completely (1 << 31 more ticks). Ths change makes it only return false if jiffies is in the small time window starting at the previous call when true was returned and ending interval_msecs later. Note that if jiffies loops completely between two calls to printk_timed_ratelimit(), it will obviously still wrongly return false, but this is something with a low probability. If something completely reliable is needed I guess jiffies_64 must be used (which this change does not do). Signed-off-by: Guillaume Knispel Cc: Ulrich Drepper Cc: Rusty Russell Cc: Andrew Morton Cc: Linus Torvalds LKML-Reference: <20090317161842.0059096b@xilun.lan.proformatique.com> Signed-off-by: Ingo Molnar --- kernel/printk.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index e3602d0755b..2be719908d1 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1292,8 +1292,11 @@ EXPORT_SYMBOL(printk_ratelimit); bool printk_timed_ratelimit(unsigned long *caller_jiffies, unsigned int interval_msecs) { - if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) { - *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs); + if (*caller_jiffies == 0 + || !time_in_range(jiffies, *caller_jiffies, + *caller_jiffies + + msecs_to_jiffies(interval_msecs))) { + *caller_jiffies = jiffies; return true; } return false; -- cgit v1.2.3 From 04d491ab2a53008a1aa98ac09561768c7f3adda3 Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Thu, 2 Apr 2009 16:58:57 -0700 Subject: kexec: add dmesg log symbols to /proc/vmcoreinfo lists It would be nice to be able to extract the dmesg log from a vmcore file without needing to keep the debug symbols for the running kernel handy all the time. We have a facility to do this in /proc/vmcore. This patch adds the log_buf and log_end symbols to the vmcoreinfo area so that tools (like makedumpfile) can easily extract the dmesg logs from a vmcore image. [akpm@linux-foundation.org: several fixes and cleanups] [akpm@linux-foundation.org: fix unused log_buf_kexec_setup()] [akpm@linux-foundation.org: build fix] Signed-off-by: Neil Horman Cc: Simon Horman Acked-by: Vivek Goyal Cc: Neil Horman Cc: Simon Horman Cc: Vivek Goyal Cc: Randy Dunlap Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index e3602d0755b..a5f61a9aced 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -32,6 +32,7 @@ #include #include #include +#include #include @@ -135,6 +136,24 @@ static char *log_buf = __log_buf; static int log_buf_len = __LOG_BUF_LEN; static unsigned logged_chars; /* Number of chars produced since last read+clear operation */ +#ifdef CONFIG_KEXEC +/* + * This appends the listed symbols to /proc/vmcoreinfo + * + * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to + * obtain access to symbols that are otherwise very difficult to locate. These + * symbols are specifically used so that utilities can access and extract the + * dmesg log from a vmcore file after a crash. + */ +void log_buf_kexec_setup(void) +{ + VMCOREINFO_SYMBOL(log_buf); + VMCOREINFO_SYMBOL(log_end); + VMCOREINFO_SYMBOL(log_buf_len); + VMCOREINFO_SYMBOL(logged_chars); +} +#endif + static int __init log_buf_len_setup(char *str) { unsigned size = memparse(str, &str); -- cgit v1.2.3