|author||KaiGai Kohei||2006-03-31 04:30:45 -0600|
|committer||Linus Torvalds||2006-03-31 14:18:54 -0600|
[PATCH] Fix pacct bug in multithreading case.
I noticed a bug on the process accounting facility. In multi-threading process, some data would be recorded incorrectly when the group_leader dies earlier than one or more threads. The attached patch fixes this problem. See below. 'bugacct' is a test program that create a worker thread after 4 seconds sleeping, then the group_leader dies soon. The worker thread consume CPU/Memory for 6 seconds, then exit. We can estimate 10 seconds as etime and 6 seconds as stime + utime. This is a sample program which the group_leader dies earlier than other threads. The results of same binary execution on different kernel are below. -- accounted records -------------------- | btime | utime | stime | etime | minflt | majflt | comm | original | 13:16:40 | 0.00 | 0.00 | 6.10 | 171 | 0 | bugacct | patched | 13:20:21 | 5.83 | 0.18 | 10.03 | 32776 | 0 | bugacct | (*) bugacct allocates 128MB memory, thus 128MB / 4KB = 32768 of minflt is appropriate. -- Test results in original kernel ------ $ date; time -p ./bugacct Tue Mar 28 13:16:36 JST 2006 <- But pacct said btime is 13:16:40 real 10.11 <- But pacct said etime is 6.10 user 5.96 <- But pacct said utime is 0.00 sys 0.14 <- But pacct said stime is 0.00 $ -- Test results in patched kernel ------- $ date; time -p ./bugacct Tue Mar 28 13:20:21 JST 2006 real 10.04 user 5.83 sys 0.19 $ In the original 2.6.16 kernel, pacct records btime, utime, stime, etime and minflt incorrectly. In my opinion, this problem is caused by an assumption that group_leader dies last. The following section calculates process running time for etime and btime. But it means running time of the thread that dies last, not process. The start_time of the first thread in the process (group_leader) should be reduced from uptime to calculate etime and btime correctly. ---- do_acct_process() in kernel/acct.c: /* calculate run_time in nsec*/ do_posix_clock_monotonic_gettime(&uptime); run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec; run_time -= (u64)current->start_time.tv_sec*NSEC_PER_SEC + current->start_time.tv_nsec; ---- The following section calculates stime and utime of the process. But it might count the utime and stime of the group_leader duplicatly and ignore the utime and stime of the thread dies last, when one or more threads remain after group_leader dead. The ac_utime should be calculated as the sum of the signal->utime and utime of the thread dies last. The ac_stime should be done also. ---- do_acct_process() in kernel/acct.c: jiffies = cputime_to_jiffies(cputime_add(current->group_leader->utime, current->signal->utime)); ac.ac_utime = encode_comp_t(jiffies_to_AHZ(jiffies)); jiffies = cputime_to_jiffies(cputime_add(current->group_leader->stime, current->signal->stime)); ac.ac_stime = encode_comp_t(jiffies_to_AHZ(jiffies)); ---- The part of the minflt/majflt calculation has same problem. This patch solves those problems, I think. Cc: Ingo Molnar <email@example.com> Signed-off-by: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
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