Re: [PATCH 4/4] printk: miscellaneous cleanups

From: Alex Elder
Date: Wed Jul 09 2014 - 12:45:56 EST

On 07/09/2014 11:29 AM, Petr Mládek wrote:
Sending once again as a correct reply. I am sorry for the
confusion. I think that it is high time for me to go home and sleep :-)

On Wed 2014-07-09 08:04:16, Alex Elder wrote:
This patch contains some small cleanups to kernel/printk/printk.c.
None of them should cause any change in behavior.
- When CONFIG_PRINTK is defined, parenthesize the value of LOG_LINE_MAX.
- When CONFIG_PRINTK is *not* defined, there is an extra LOG_LINE_MAX
definition; delete it.
- Pull an assignment out of a conditional expression in console_setup().
- Use isdigit() in console_setup() rather than open coding it.
- In update_console_cmdline(), drop a NUL-termination assignment;
the strlcpy() call that precedes it guarantees it's not needed.
- Simplify some logic in printk_timed_ratelimit().

Signed-off-by: Alex Elder <elder@xxxxxxxxxx>
kernel/printk/printk.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6f75e8a..909029e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c

. . .

@@ -2611,14 +2612,13 @@ EXPORT_SYMBOL(__printk_ratelimit);
bool printk_timed_ratelimit(unsigned long *caller_jiffies,
unsigned int 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;
+ unsigned long elapsed = jiffies - *caller_jiffies;

Currently, all callers pass a 0 value in *caller_jiffies
initially (using a static/BSS variable), and a value updated
by a previous call to __printk_ratelimit() thereafter.

If a caller passed something different, yes, it's possible the
result would wrap to a high unsigned value (i.e., go negative).
However the logic used here involves the same subtraction
operation as was used before--though previously that was
buried inside the time_after() macro called by time_in_range().


I wondered if the deduction might be negative. Well, it should not be
if none manipulates *caller_jiffies in a strange way. If it happens,
the following condition will most likely fail and *caller_jiffies will
get reset to jiffies. It looks reasonable to me.

Reviewed-by: Petr Mladek <pmladek@xxxxxxx>

+ if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
+ return false;
+ *caller_jiffies = jiffies;
+ return true;

Best Regards,

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