[systemd-devel] [PATCH] systemd-bootchart: Prevent closing random file descriptors
Alexander Sverdlin
alexander.sverdlin at gmail.com
Sat Mar 28 18:13:15 PDT 2015
If the kernel has no CONFIG_SCHED_DEBUG option set, systemd-bootchart produces
empty .svg file. The reason for this is very fragile file descriptor logic in
log_sample() and main() (/* do some cleanup, close fd's */ block). There are
many places where file descriptors are closed on failure (missing SCHED_DEBUG
provokes it), but there are several problems with it:
- following iterations in the loop see that the descriptor is non zero and do
not open the corresponding file again;
- "some cleanup" code closes already closed files and the descriptors are reused
already, in particular for resulting .svg file;
- static "vmstat" and "schedstat" variables in log_sample() made the situation
even worse.
These are the strace fragments:
[...]
close(7) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
pread(7, 0xbea60a2c, 4095, 0) = -1 EBADF (Bad file descriptor)
close(7) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
pread(7, 0xbea60a2c, 4095, 0) = -1 EBADF (Bad file descriptor)
close(7) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
getdents64(4, /* 0 entries */, 32768) = 0
clock_gettime(CLOCK_MONOTONIC, {24, 783843501}) = 0
nanosleep({0, 5221792}, NULL) = 0
clock_gettime(CLOCK_MONOTONIC, {24, 789726835}) = 0
lseek(4, 0, SEEK_SET) = 0
pread(5, "nr_free_pages 52309\nnr_alloc_bat"..., 4095, 0) = 685
pread(6, "version 15\ntimestamp 4294939775\n"..., 4095, 0) = 86
getdents64(4, /* 99 entries */, 32768) = 2680
pread(7, 0xbea60a2c, 4095, 0) = -1 EBADF (Bad file descriptor)
close(7) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
pread(8, 0xbea60a2c, 4095, 0) = -1 EBADF (Bad file descriptor)
close(8) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
pread(9, 0xbea60a2c, 4095, 0) = -1 EBADF (Bad file descriptor)
close(9) = -1 EBADF (Bad file descriptor)
[...]
where it obviously tries to close same and reused decriptors many times, also
passing return code "-1" instead of descriptor...
[...]
close(7) = -1 EBADF (Bad file descriptor)
close(-1) = -1 EBADF (Bad file descriptor)
pipe2([7, 8], O_CLOEXEC) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xb6fd0068) = 192
close(8) = 0
fcntl64(7, F_SETFD, 0) = 0
fstat64(7, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6fd2000
read(7, "[ 0.074507] calling vfp_init"..., 4096) = 4096
[...]
read(7, "s)\n[ 6.228910] UBIFS: reserve"..., 4096) = 4096
read(7, "trary Executable File Formats Fi"..., 4096) = 1616
read(7, "", 4096) = 0
close(7) = 0
wait4(192, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 192
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=192, si_uid=0, si_status=0, si_utime=9, si_stime=9} ---
munmap(0xb6fd2000, 4096) = 0
fstat64(7, 0xbea62850) = -1 EBADF (Bad file descriptor)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6fce000
write(7, "<?xml version=\"1.0\" standalone=\""..., 38) = -1 EBADF (Bad file descriptor)
write(7, "<!DOCTYPE svg PUBLIC \"-//W3C//DT"..., 47) = -1 EBADF (Bad file descriptor)
write(7, "\"http://www.w3.org/Graphics/SVG/"..., 52) = -1 EBADF (Bad file descriptor)
[...]
here .svg file had descriptor 7, but was closed by log_sample(), then even reused
to read /proc entry and finally systemd-bootchart even tries to write .svg file, but
descriptor is long time lost already.
Fix it by zeroing all the closed descriptors immediately, this would repair
existing caching of open files and clean-up strategy.
The fix is important even with CONFIG_SCHED_DEBUG option enabled, because very
first failure to open /proc/<pid>/* because process exited will result in some
other victim descriptor being closed later and will therefore disturb the whole
collected statistics.
---
src/bootchart/store.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/src/bootchart/store.c b/src/bootchart/store.c
index dfa681f..8525f62 100644
--- a/src/bootchart/store.c
+++ b/src/bootchart/store.c
@@ -152,6 +152,7 @@ void log_sample(int sample, struct list_sample_data **ptr) {
n = pread(vmstat, buf, sizeof(buf) - 1, 0);
if (n <= 0) {
close(vmstat);
+ vmstat = 0;
return;
}
buf[n] = '\0';
@@ -184,6 +185,7 @@ vmstat_next:
n = pread(schedstat, buf, sizeof(buf) - 1, 0);
if (n <= 0) {
close(schedstat);
+ schedstat = 0;
return;
}
buf[n] = '\0';
@@ -286,6 +288,7 @@ schedstat_next:
s = pread(ps->sched, buf, sizeof(buf) - 1, 0);
if (s <= 0) {
close(ps->sched);
+ ps->sched = 0;
continue;
}
buf[s] = '\0';
@@ -387,8 +390,11 @@ schedstat_next:
if (s <= 0) {
/* clean up our file descriptors - assume that the process exited */
close(ps->schedstat);
- if (ps->sched)
+ ps->schedstat = 0;
+ if (ps->sched) {
close(ps->sched);
+ ps->sched = 0;
+ }
//if (ps->smaps)
// fclose(ps->smaps);
continue;
@@ -488,8 +494,11 @@ catch_rename:
if (s <= 0) {
/* clean up file descriptors */
close(ps->sched);
- if (ps->schedstat)
+ ps->sched = 0;
+ if (ps->schedstat) {
close(ps->schedstat);
+ ps->schedstat = 0;
+ }
//if (ps->smaps)
// fclose(ps->smaps);
continue;
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