From 9fa896f9e48f54efce4a44bd5e1310b442283da7 Mon Sep 17 00:00:00 2001 From: Balazs Benics Date: Wed, 2 Feb 2022 12:55:44 +0100 Subject: [PATCH] [scan-build] Fix deadlock at failures in libears/ear.c We experienced some deadlocks when we used multiple threads for logging using `scan-builds` intercept-build tool when we used multiple threads by e.g. logging `make -j16` ``` (gdb) bt #0 0x00007f2bb3aff110 in __lll_lock_wait () from /lib/x86_64-linux-gnu/libpthread.so.0 #1 0x00007f2bb3af70a3 in pthread_mutex_lock () from /lib/x86_64-linux-gnu/libpthread.so.0 #2 0x00007f2bb3d152e4 in ?? () #3 0x00007ffcc5f0cc80 in ?? () #4 0x00007f2bb3d2bf5b in ?? () from /lib64/ld-linux-x86-64.so.2 #5 0x00007f2bb3b5da27 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 #6 0x00007f2bb3b5dbe0 in exit () from /lib/x86_64-linux-gnu/libc.so.6 #7 0x00007f2bb3d144ee in ?? () #8 0x746e692f706d742f in ?? () #9 0x692d747065637265 in ?? () #10 0x2f653631326b3034 in ?? () #11 0x646d632e35353532 in ?? () #12 0x0000000000000000 in ?? () ``` I think the gcc's exit call caused the injected `libear.so` to be unloaded by the `ld`, which in turn called the `void on_unload() __attribute__((destructor))`. That tried to acquire an already locked mutex which was left locked in the `bear_report_call()` call, that probably encountered some error and returned early when it forgot to unlock the mutex. All of these are speculation since from the backtrace I could not verify if frames 2 and 3 are in fact corresponding to the `libear.so` module. But I think it's a fairly safe bet. So, hereby I'm releasing the held mutex on *all paths*, even if some failure happens. PS: I would use lock_guards, but it's C. Reviewed-by: NoQ Differential Revision: https://reviews.llvm.org/D118439 (cherry picked from commit d919d027ba2a41df5d51ce82ae7f2fb64d2cba41) --- clang/tools/scan-build-py/lib/libear/ear.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/clang/tools/scan-build-py/lib/libear/ear.c b/clang/tools/scan-build-py/lib/libear/ear.c index b06ec7ab000401..94cb865bd0cab7 100644 --- a/clang/tools/scan-build-py/lib/libear/ear.c +++ b/clang/tools/scan-build-py/lib/libear/ear.c @@ -411,6 +411,7 @@ static void bear_report_call(char const *fun, char const *const argv[]) { const char *cwd = getcwd(NULL, 0); if (0 == cwd) { perror("bear: getcwd"); + pthread_mutex_unlock(&mutex); exit(EXIT_FAILURE); } char const *const out_dir = initial_env[0]; @@ -419,11 +420,13 @@ static void bear_report_call(char const *fun, char const *const argv[]) { if (-1 == snprintf(filename, path_max_length, "%s/%d.cmd", out_dir, getpid())) { perror("bear: snprintf"); + pthread_mutex_unlock(&mutex); exit(EXIT_FAILURE); } FILE *fd = fopen(filename, "a+"); if (0 == fd) { perror("bear: fopen"); + pthread_mutex_unlock(&mutex); exit(EXIT_FAILURE); } fprintf(fd, "%d%c", getpid(), RS); @@ -437,6 +440,7 @@ static void bear_report_call(char const *fun, char const *const argv[]) { fprintf(fd, "%c", GS); if (fclose(fd)) { perror("bear: fclose"); + pthread_mutex_unlock(&mutex); exit(EXIT_FAILURE); } free((void *)cwd);