Hi,
Gyula FARKAS wrote,
> Hello,
>
> We have noticed random deadlocks in malloc/free when using uClibc-ng +
> Thumb1 + NPTL compiled for ARMv6 in multi-threaded environment.
Your example segfaults directly for me under qemu-system-arm or even
on Debian/amd64 with gibc. Is it possible the code is broken?
best regards
Waldemar
> Steps to reproduce
>
> 1. Build Buildroot 2019.02.9 SDK with the following configuration:
>
> BR2_arm=y
> BR2_arm1176jz_s=y
> BR2_ARM_INSTRUCTIONS_THUMB=y
> BR2_SHARED_STATIC_LIBS=y
> BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
> BR2_TOOLCHAIN_BUILDROOT_USE_SSP=y
> BR2_TOOLCHAIN_BUILDROOT_CXX=y
>
> 2. Cross compile the sample (see below) application with the SDK using
> static linking:
>
> $ arm-buildroot-linux-uclibcgnueabi-gcc -static -g deadlock.c \
> -lpthread -o deadlock
>
> 3. Run the application with at least two threads
>
> 3.1. Run the application using QEMU static emulation:
>
> $ qemu-arm-static ./deadlock 4 1000000
>
> 3.2. Run the application on a device with ARMv6 support (ex. any RPi
> with Raspbian image):
>
> $ ./deadlock 4 1000000
>
> Expected results:
>
> The application should always exit cleanly.
>
> Actual results:
>
> The application often deadlocks in both cases.
>
>
> Notes:
>
> 1. The bug is also reproducible with latest uClibc-ng (v1.0.32)
>
> 2. According to our tests the endianness does not matter
>
> 3. The callstack when deadlock appears:
>
> (gdb) info threads
> Id Target Id Frame
> * 1 LWP 11653 "mutex" 0x000165b2 in pthread_join ()
> 2 LWP 11656 "mutex" 0x00014cac in __lll_lock_wait ()
> 3 LWP 11657 "mutex" 0x00014ce2 in __lll_lock_wait ()
> 4 LWP 11658 "mutex" 0x00014cac in __lll_lock_wait ()
> 5 LWP 11659 "mutex" 0x00014cac in __lll_lock_wait ()
>
> (gdb) t 1
> [Switching to thread 1 (LWP 11653)]
> #0 0x000165b2 in pthread_join ()
>
> (gdb) bt
> #0 0x000165b2 in pthread_join ()
> #1 0x00010396 in main (argc=3, argv=0x7efff784) at deadlock.c:42
>
> (gdb) t 2
> [Switching to thread 2 (LWP 11656)]
> #0 0x00014cac in __lll_lock_wait ()
>
> (gdb) bt
> #0 0x00014cac in __lll_lock_wait ()
> #1 0x00016b7e in pthread_mutex_lock ()
> #2 0x0001199e in __libc_malloc ()
> #3 0x00010278 in do_request (data=0x1) at deadlock.c:13
> #4 0x00015b36 in start_thread ()
> #5 0x000173f4 in clone ()
>
> (gdb) t 3
> [Switching to thread 3 (LWP 11657)]
> #0 0x00014ce2 in __lll_lock_wait ()
>
> (gdb) bt
> #0 0x00014ce2 in __lll_lock_wait ()
> #1 0x00016b7e in pthread_mutex_lock ()
> #2 0x000117c2 in __libc_free ()
> #3 0x00010284 in do_request (data=0x2) at deadlock.c:15
> #4 0x00015b36 in start_thread ()
> #5 0x000173f4 in clone ()
>
> (gdb) t 4
> [Switching to thread 4 (LWP 11658)]
> #0 0x00014cac in __lll_lock_wait ()
>
> (gdb) bt
> #0 0x00014cac in __lll_lock_wait ()
> #1 0x00016b7e in pthread_mutex_lock ()
> #2 0x0001199e in __libc_malloc ()
> #3 0x00010278 in do_request (data=0x3) at deadlock.c:13
> #4 0x00015b36 in start_thread ()
> #5 0x000173f4 in clone ()
>
> (gdb) t 5
> [Switching to thread 5 (LWP 11659)]
> #0 0x00014cac in __lll_lock_wait ()
>
> (gdb) bt
> #0 0x00014cac in __lll_lock_wait ()
> #1 0x00016b7e in pthread_mutex_lock ()
> #2 0x0001199e in __libc_malloc ()
> #3 0x00010278 in do_request (data=0x4) at deadlock.c:13
> #4 0x00015b36 in start_thread ()
> #5 0x000173f4 in clone ()
>
> Sample application:
>
> #include <stdlib.h>
> #include <stdio.h>
> #include <pthread.h>
>
> int count;
>
> void *do_request(void *data)
> {
> for (int i = 0; i < count; i++) {
> if (i % 1000 == 0)
> printf("Alloc for %p count %d\n", data, i);
> char *buffer = malloc(32 * sizeof(char));
>
> free(buffer);
> }
> return NULL;
> }
>
> int main(int argc, char *argv[])
> {
> int i, rc;
> int threads_count = atoi(argv[1]);
>
> count = atoi(argv[2]);
>
> pthread_t threads[threads_count];
> printf("Creating %d threads\n", threads_count);
>
> for (i = 0; i < threads_count; i++) {
> rc = pthread_create(&threads[i], NULL, do_request, (int*)(i+1));
>
> if (rc) {
> printf("Error creating thread\n");
> exit(1);
> }
> }
>
> for (i = 0; i < threads_count; i++)
> if (pthread_join(threads[i], NULL)) {
> printf("Error joining thread\n");
> exit(1);
> }
>
> printf("Done. \n");
> return 0;
> }
>
>
> Best regards,
> Gyula Farkas
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