Documentation/timers/timers-howto.txt outlines the intended usage of usleep_range(), this spatch tries to locate missuse/out-of-spec cases.
Signed-off-by: Nicholas Mc Guire <[email protected]> --- V2: added context mode as suggested by Julia Lawall <[email protected]> added min<max case sugested by Joe Perches <[email protected]> added in the range checks as they are resonably reliable based on a review of all 1648 call sites of usleep_range() 1648 calls total 1488 pass numeric values only (90.29%) 27 min below 10us (1.81%) 40 min above 10ms (2.68%) min out of spec 4.50% 76 preprocessor constants (4.61%) 1 min below 10us (1.31%) 8 min above 10ms (10.52%) min out of spec 11.84% 85 expressions (5.15%) 1(0) min below 10us (1.50%)* 6(2) min above 10ms (7.50%)* min out of spec 9.0% Errors: 23 where min==max (1.39%) 0 where max < min (0.00%) Total: Bugs: 6.48%-10.70%* Crit: 3.09%-3.15%* (min < 10, min==max, max < min) Detectable by coccinelle: Bugs: 74/103 (71.8%) Crit: 50/52 (96.1%) * numbers estimated based on code review Patch is againts 4.9.0 (localversion-next is next-20161214) scripts/coccinelle/api/bad_usleep_range.cocci | 88 +++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 scripts/coccinelle/api/bad_usleep_range.cocci diff --git a/scripts/coccinelle/api/bad_usleep_range.cocci b/scripts/coccinelle/api/bad_usleep_range.cocci new file mode 100644 index 0000000..003e9ef --- /dev/null +++ b/scripts/coccinelle/api/bad_usleep_range.cocci @@ -0,0 +1,88 @@ +/// report bad/problematic usleep_range usage +// +// This is a checker for the documented intended use of usleep_range +// see: Documentation/timers/timers-howto.txt and +// Link: http://lkml.org/lkml/2016/11/29/54 for some notes on +// when mdelay might not be a suitable replacement +// +// Limitations: +// * The numeric limits are only checked when numeric constants are in +// use (as of 4.9.0 thats 90.29% of the calls) no constant folding +// is done - so this can miss some out-of-range cases - but in 4.9.0 +// it was catching 74 of the 103 bad cases (71.8%) and 50 of 52 +// (96.1%) of the critical cases (min < 10 and min==max - there +// * There may be RT use-cases where both min < 10 and min==max) +// justified (e.g. high-throughput drivers on a shielded core) +// +// 1) warn if min == max +// +// The problem is that usleep_range is calculating the delay by +// exp = ktime_add_us(ktime_get(), min) +// delta = (u64)(max - min) * NSEC_PER_USEC +// so delta is set to 0 if min==max +// and then calls +// schedule_hrtimeout_range(exp, 0,...) +// effectively this means that the clock subsystem has no room to +// optimize. usleep_range() is in non-atomic context so a 0 range +// makes very little sense as the task can be preempted anyway so +// there is no guarantee that the 0 range would be adding much +// precision - it just removes optimization potential, so it probably +// never really makes sense. +// +// 2) warn if min < 10 or min > 20ms +// +// it makes little sense to use a non-atomic call for very short +// delays because the scheduling jitter will most likely exceed +// this limit - udelay() makes more sense in that case. For very +// large delays using hrtimers is useless as preemption becomes +// quite likely resulting in high inaccuracy anyway - so use +// jiffies based msleep and don't burden the hrtimer subsystem. +// +// 3) warn if max < min +// +// Joe Perches <[email protected]> added a check for this case +// that is definitely wrong. +// +// Confidence: Moderate +// Copyright: (C) 2016 Nicholas Mc Guire, OSADL. GPLv2. +// Comments: +// Options: --no-includes --include-headers + +virtual org +virtual report +virtual context + +@nullrangectx depends on context@ +expression E1,E2; +position p; +@@ + +* usleep_range@p(E1,E2) + + +@nullrange@ +expression E1,E2; +position p; +@@ + + usleep_range@p(E1,E2) + +@script:python depends on !context@ +p << nullrange.p; +min << nullrange.E1; +max << nullrange.E2; +@@ + +if(min == max): + msg = "WARNING: usleep_range min == max (%s) - consider delta " % (min) + coccilib.report.print_report(p[0], msg) +if str.isdigit(min): + if(int(min) < 10): + msg = "ERROR: usleep_range min (%s) less than 10us - consider using udelay()" % (min) + coccilib.report.print_report(p[0], msg) + if(20000 < int(min)): + msg = "ERROR: usleep_range min (%s) exceed 20m - consider using mslee()" % (min) + coccilib.report.print_report(p[0], msg) + if(int(max) < int(min)): + msg = "ERROR: usleep_range max (%s) less than min (%s)" % (max,min) + coccilib.report.print_report(p[0], msg) -- 2.1.4
