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zed: protect against wait4()/fork() races to the global PID table 

This can be very easily triggered by adding a sleep(1) before
the wait4() on a PID-starved system: the reaper thread would wait
for a child before its entry appeared, letting old entries accumulate:

  Invoking "all-debug.sh" eid=3021 pid=391
  Finished "(null)" eid=0 pid=391 time=0.002432s exit=0
  Invoking "all-syslog.sh" eid=3021 pid=336
  Finished "(null)" eid=0 pid=336 time=0.002432s exit=0
  Invoking "history_event-zfs-list-cacher.sh" eid=3021 pid=347
  Invoking "all-debug.sh" eid=3022 pid=349
  Finished "history_event-zfs-list-cacher.sh" eid=3021 pid=347
                                              time=0.001669s exit=0
  Finished "(null)" eid=0 pid=349 time=0.002404s exit=0
  Invoking "all-syslog.sh" eid=3022 pid=370
  Finished "(null)" eid=0 pid=370 time=0.002427s exit=0
  Invoking "history_event-zfs-list-cacher.sh" eid=3022 pid=391
  avl_find(tree, new_node, &where) == NULL
  ASSERT at ../../module/avl/avl.c:641:avl_add()
  Thread 1 "zed" received signal SIGABRT, Aborted.

By employing this wider lock, we atomise [wait, remove] and [fork, add]:
slowing down the reaper thread now just causes some zombies
to accumulate until it can get to them

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11963
Closes #11965
This commit is contained in:
наб 2021-05-08 00:10:16 +02:00 committed by GitHub
parent c074a7de13
commit 3bd6b0e05a
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1 changed files with 7 additions and 6 deletions
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13
cmd/zed/zed_exec.c
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@ -142,8 +142,10 @@ _zed_exec_fork_child(uint64_t eid, const char *dir, const char *prog,
prog, eid, strerror(ENAMETOOLONG)); prog, eid, strerror(ENAMETOOLONG));
return; return;
} }
(void) pthread_mutex_lock(&_launched_processes_lock);
pid = fork(); pid = fork();
if (pid < 0) { if (pid < 0) {
(void) pthread_mutex_unlock(&_launched_processes_lock);
zed_log_msg(LOG_WARNING, zed_log_msg(LOG_WARNING,
"Failed to fork \"%s\" for eid=%llu: %s", "Failed to fork \"%s\" for eid=%llu: %s",
prog, eid, strerror(errno)); prog, eid, strerror(errno));
@ -166,20 +168,19 @@ _zed_exec_fork_child(uint64_t eid, const char *dir, const char *prog,
/* parent process */ /* parent process */
__atomic_sub_fetch(&_launched_processes_limit, 1, __ATOMIC_SEQ_CST);
zed_log_msg(LOG_INFO, "Invoking \"%s\" eid=%llu pid=%d",
prog, eid, pid);
node = calloc(1, sizeof (*node)); node = calloc(1, sizeof (*node));
if (node) { if (node) {
node->pid = pid; node->pid = pid;
node->eid = eid; node->eid = eid;
node->name = strdup(prog); node->name = strdup(prog);
(void) pthread_mutex_lock(&_launched_processes_lock);
avl_add(&_launched_processes, node); avl_add(&_launched_processes, node);
(void) pthread_mutex_unlock(&_launched_processes_lock);
} }
(void) pthread_mutex_unlock(&_launched_processes_lock);
__atomic_sub_fetch(&_launched_processes_limit, 1, __ATOMIC_SEQ_CST);
zed_log_msg(LOG_INFO, "Invoking \"%s\" eid=%llu pid=%d",
prog, eid, pid);
} }
static void static void