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Threadproof our log_backtrace implementation

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It's possible for two threads to hit assertion failures at the same
time.  If that happens, let's keep them from stomping on the same
cb_buf field.

Fixes bug 11048; bugfix on 0.2.5.2-alpha. Reported by "cypherpunks".
This commit is contained in:
Nick Mathewson 2014-02-24 12:15:32 -05:00
parent 1753975ece
commit a3ab31f5dc
2 changed files with 26 additions and 4 deletions
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8
changes/bug11048 Normal file
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@ -0,0 +1,8 @@
o Minor bugfixes:
- Avoid strange behavior if two threads hit failed asswertions
at the same time and both try to log backtraces at
once. (Previously, if this had happened, both threads would
have stored their intermediate results in the same buffer, and
generated junk outputs.) Reported by "cypherpunks". Fixes bug
11048; bugfix on 0.2.5.2-alpha.

22
src/common/backtrace.c
View File

@ -49,6 +49,8 @@ static char *bt_version = NULL;
/** Static allocation of stack to dump. This is static so we avoid stack /** Static allocation of stack to dump. This is static so we avoid stack
* pressure. */ * pressure. */
static void *cb_buf[MAX_DEPTH]; static void *cb_buf[MAX_DEPTH];
/** Protects cb_buf_mutex from concurrent access */
static tor_mutex_t cb_buf_mutex;
/** Change a stacktrace in <b>stack</b> of depth <b>depth</b> so that it will /** Change a stacktrace in <b>stack</b> of depth <b>depth</b> so that it will
* log the correct function from which a signal was received with context * log the correct function from which a signal was received with context
@ -84,18 +86,27 @@ clean_backtrace(void **stack, int depth, const ucontext_t *ctx)
void void
log_backtrace(int severity, int domain, const char *msg) log_backtrace(int severity, int domain, const char *msg)
{ {
int depth = backtrace(cb_buf, MAX_DEPTH); int depth;
char **symbols = backtrace_symbols(cb_buf, depth); char **symbols;
int i; int i;
tor_mutex_acquire(&cb_buf_mutex);
depth = backtrace(cb_buf, MAX_DEPTH);
symbols = backtrace_symbols(cb_buf, depth);
tor_log(severity, domain, "%s. Stack trace:", msg); tor_log(severity, domain, "%s. Stack trace:", msg);
if (!symbols) { if (!symbols) {
tor_log(severity, domain, " Unable to generate backtrace."); tor_log(severity, domain, " Unable to generate backtrace.");
return; goto done;
} }
for (i=0; i < depth; ++i) { for (i=0; i < depth; ++i) {
tor_log(severity, domain, " %s", symbols[i]); tor_log(severity, domain, " %s", symbols[i]);
} }
free(symbols); free(symbols);
done:
tor_mutex_release(&cb_buf_mutex);
} }
static void crash_handler(int sig, siginfo_t *si, void *ctx_) static void crash_handler(int sig, siginfo_t *si, void *ctx_)
@ -140,6 +151,9 @@ install_bt_handler(void)
int i, rv=0; int i, rv=0;
struct sigaction sa; struct sigaction sa;
tor_mutex_init(&cb_buf_mutex);
memset(&sa, 0, sizeof(sa)); memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = crash_handler; sa.sa_sigaction = crash_handler;
sa.sa_flags = SA_SIGINFO; sa.sa_flags = SA_SIGINFO;
@ -158,7 +172,7 @@ install_bt_handler(void)
static void static void
remove_bt_handler(void) remove_bt_handler(void)
{ {
/* We don't need to actually free anything at exit here. */ tor_mutex_uninit(&cb_buf_mutex);
} }
#endif #endif