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tools subcmd: Robust fallback and existence checks for process reaping

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Update check_if_command_finished() and wait_or_whine() to handle invalid
PIDs gracefully (<= 0) by setting cmd->finished = 1 and returning early.
This avoids executing waitpid(-1, ...) or waitpid(0, ...) downstream,
which can block or reap parallel tests' exit status causing state
corruption.

Introduce a fallback mechanism in check_if_command_finished() using
waitpid(..., WNOHANG) when /proc/<pid>/status is inaccessible (e.g. due
to EMFILE/ENFILE) to safely check and reap finished children.

Assisted-by: Gemini-CLI:Google Gemini 3
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ian Rogers
2026-06-02 10:41:18 -07:00
committed by Arnaldo Carvalho de Melo
parent 8ae26f6ae7
commit c7dacfb87b
1 changed files with 65 additions and 4 deletions
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69
tools/lib/subcmd/run-command.c
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@@ -169,8 +169,18 @@ int start_command(struct child_process *cmd)
static int wait_or_whine(struct child_process *cmd, bool block)
{
bool finished = cmd->finished;
int result = cmd->finish_result;
bool finished;
int result;
if (cmd->pid <= 0) {
cmd->finished = 1;
if (cmd->pid < 0 && cmd->finish_result == 0)
cmd->finish_result = -ERR_RUN_COMMAND_FORK;
return cmd->finish_result;
}
finished = cmd->finished;
result = cmd->finish_result;
while (!finished) {
int status, code;
@@ -233,7 +243,18 @@ int check_if_command_finished(struct child_process *cmd)
char filename[6 + MAX_STRLEN_TYPE(typeof(cmd->pid)) + 7 + 1];
char status_line[256];
FILE *status_file;
#endif
if (cmd->finished)
return 1;
if (cmd->pid <= 0) {
cmd->finished = 1;
if (cmd->pid < 0 && cmd->finish_result == 0)
cmd->finish_result = -ERR_RUN_COMMAND_FORK;
return 1;
}
#ifdef __linux__
/*
* Check by reading /proc/<pid>/status as calling waitpid causes
* stdout/stderr to be closed and data lost.
@@ -241,8 +262,48 @@ int check_if_command_finished(struct child_process *cmd)
sprintf(filename, "/proc/%u/status", cmd->pid);
status_file = fopen(filename, "r");
if (status_file == NULL) {
/* Open failed assume finish_command was called. */
return true;
int status;
pid_t waiting;
/*
* fopen() can fail with ENOENT if the process has been reaped.
* It can also fail with EMFILE/ENFILE if RLIMIT_NOFILE is reached.
* In those cases, use waitpid(..., WNOHANG) to robustly check
* and reap the process if it has exited.
*/
if (errno == ENOENT)
return 1;
waiting = waitpid(cmd->pid, &status, WNOHANG);
if (waiting == cmd->pid) {
int result;
int code;
cmd->finished = 1;
if (WIFSIGNALED(status)) {
result = -ERR_RUN_COMMAND_WAITPID_SIGNAL;
} else if (!WIFEXITED(status)) {
result = -ERR_RUN_COMMAND_WAITPID_NOEXIT;
} else {
code = WEXITSTATUS(status);
switch (code) {
case 127:
result = -ERR_RUN_COMMAND_EXEC;
break;
case 0:
result = 0;
break;
default:
result = -code;
break;
}
}
cmd->finish_result = result;
return 1;
}
if (waiting < 0 && (errno == ECHILD || errno == ESRCH))
return 1;
return 0;
}
while (fgets(status_line, sizeof(status_line), status_file) != NULL) {
char *p;