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authorKaiGai Kohei <kaigai@ak.jp.nec.com>2006-03-31 10:30:45 (GMT)
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-31 20:18:54 (GMT)
commitbb231fe3a53b2d34c1aef119613816fcb18864b1 (patch)
tree55e686f0118aebedec1a6ddf52746a8a722b51cc /kernel
parentf79e2abb9bd452d97295f34376dedbec9686b986 (diff)
downloadlinux-bb231fe3a53b2d34c1aef119613816fcb18864b1.tar.xz
[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 <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/acct.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/kernel/acct.c b/kernel/acct.c
index 065d8b4..b327f4d 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -449,8 +449,8 @@ static void do_acct_process(long exitcode, struct file *file)
/* 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;
+ run_time -= (u64)current->group_leader->start_time.tv_sec * NSEC_PER_SEC
+ + current->group_leader->start_time.tv_nsec;
/* convert nsec -> AHZ */
elapsed = nsec_to_AHZ(run_time);
#if ACCT_VERSION==3
@@ -469,10 +469,10 @@ static void do_acct_process(long exitcode, struct file *file)
#endif
do_div(elapsed, AHZ);
ac.ac_btime = xtime.tv_sec - elapsed;
- jiffies = cputime_to_jiffies(cputime_add(current->group_leader->utime,
+ jiffies = cputime_to_jiffies(cputime_add(current->utime,
current->signal->utime));
ac.ac_utime = encode_comp_t(jiffies_to_AHZ(jiffies));
- jiffies = cputime_to_jiffies(cputime_add(current->group_leader->stime,
+ jiffies = cputime_to_jiffies(cputime_add(current->stime,
current->signal->stime));
ac.ac_stime = encode_comp_t(jiffies_to_AHZ(jiffies));
/* we really need to bite the bullet and change layout */
@@ -522,9 +522,9 @@ static void do_acct_process(long exitcode, struct file *file)
ac.ac_io = encode_comp_t(0 /* current->io_usage */); /* %% */
ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
ac.ac_minflt = encode_comp_t(current->signal->min_flt +
- current->group_leader->min_flt);
+ current->min_flt);
ac.ac_majflt = encode_comp_t(current->signal->maj_flt +
- current->group_leader->maj_flt);
+ current->maj_flt);
ac.ac_swaps = encode_comp_t(0);
ac.ac_exitcode = exitcode;