Hi Tao, thank you for the patch.
On 2025/06/25 11:23, Tao Liu wrote: > A vmcore corrupt issue has been noticed in powerpc arch [1]. It can be > reproduced with upstream makedumpfile. > > When analyzing the corrupt vmcore using crash, the following error > message will output: > > crash: compressed kdump: uncompress failed: 0 > crash: read error: kernel virtual address: c0001e2d2fe48000 type: > "hardirq thread_union" > crash: cannot read hardirq_ctx[930] at c0001e2d2fe48000 > crash: compressed kdump: uncompress failed: 0 > > If the vmcore is generated without num-threads option, then no such > errors are noticed. > > With --num-threads=N enabled, there will be N sub-threads created. All > sub-threads are producers which responsible for mm page processing, e.g. > compression. The main thread is the consumer which responsible for > writing the compressed data into file. page_flag_buf->ready is used to > sync main and sub-threads. When a sub-thread finishes page processing, > it will set ready flag to be FLAG_READY. In the meantime, main thread > looply check all threads of the ready flags, and break the loop when > find FLAG_READY. I've tried to reproduce the issue, but I couldn't on x86_64. Do you have any possible scenario that breaks a vmcore? I could not think of it only by looking at the code. and this is just out of curiosity, is the issue reproduced with makedumpfile compiled with -O0 too? Thanks, Kazu > > page_flag_buf->ready is read/write by main/sub-threads simultaneously, > but it is unprotected and unsafe. I have tested both mutex and atomic_rw > can fix this issue. This patch takes atomic_rw for its simplicity. > > [1]: https://github.com/makedumpfile/makedumpfile/issues/15 > > Tested-by: Sourabh Jain <sourabhj...@linux.ibm.com> > Signed-off-by: Tao Liu <l...@redhat.com> > --- > > v2 -> v1: Add error message of crash into commit log > > --- > makedumpfile.c | 21 ++++++++++++++------- > 1 file changed, 14 insertions(+), 7 deletions(-) > > diff --git a/makedumpfile.c b/makedumpfile.c > index 2d3b08b..bac45c2 100644 > --- a/makedumpfile.c > +++ b/makedumpfile.c > @@ -8621,7 +8621,8 @@ kdump_thread_function_cyclic(void *arg) { > > while (buf_ready == FALSE) { > pthread_testcancel(); > - if (page_flag_buf->ready == FLAG_READY) > + if (__atomic_load_n(&page_flag_buf->ready, > + __ATOMIC_SEQ_CST) == FLAG_READY) > continue; > > /* get next dumpable pfn */ > @@ -8637,7 +8638,8 @@ kdump_thread_function_cyclic(void *arg) { > info->current_pfn = pfn + 1; > > page_flag_buf->pfn = pfn; > - page_flag_buf->ready = FLAG_FILLING; > + __atomic_store_n(&page_flag_buf->ready, FLAG_FILLING, > + __ATOMIC_SEQ_CST); > pthread_mutex_unlock(&info->current_pfn_mutex); > sem_post(&info->page_flag_buf_sem); > > @@ -8726,7 +8728,8 @@ kdump_thread_function_cyclic(void *arg) { > page_flag_buf->index = index; > buf_ready = TRUE; > next: > - page_flag_buf->ready = FLAG_READY; > + __atomic_store_n(&page_flag_buf->ready, FLAG_READY, > + __ATOMIC_SEQ_CST); > page_flag_buf = page_flag_buf->next; > > } > @@ -8855,7 +8858,8 @@ write_kdump_pages_parallel_cyclic(struct cache_data > *cd_header, > * current_pfn is used for recording the value of pfn > when checking the pfn. > */ > for (i = 0; i < info->num_threads; i++) { > - if (info->page_flag_buf[i]->ready == > FLAG_UNUSED) > + if > (__atomic_load_n(&info->page_flag_buf[i]->ready, > + __ATOMIC_SEQ_CST) == > FLAG_UNUSED) > continue; > temp_pfn = info->page_flag_buf[i]->pfn; > > @@ -8863,7 +8867,8 @@ write_kdump_pages_parallel_cyclic(struct cache_data > *cd_header, > * count how many threads have reached the end. > */ > if (temp_pfn >= end_pfn) { > - info->page_flag_buf[i]->ready = > FLAG_UNUSED; > + > __atomic_store_n(&info->page_flag_buf[i]->ready, > + FLAG_UNUSED, __ATOMIC_SEQ_CST); > end_count++; > continue; > } > @@ -8885,7 +8890,8 @@ write_kdump_pages_parallel_cyclic(struct cache_data > *cd_header, > * If the page_flag_buf is not ready, the pfn recorded > may be changed. > * So we should recheck. > */ > - if (info->page_flag_buf[consuming]->ready != > FLAG_READY) { > + if > (__atomic_load_n(&info->page_flag_buf[consuming]->ready, > + __ATOMIC_SEQ_CST) != FLAG_READY) { > clock_gettime(CLOCK_MONOTONIC, &new); > if (new.tv_sec - last.tv_sec > WAIT_TIME) { > ERRMSG("Can't get data of pfn.\n"); > @@ -8927,7 +8933,8 @@ write_kdump_pages_parallel_cyclic(struct cache_data > *cd_header, > goto out; > page_data_buf[index].used = FALSE; > } > - info->page_flag_buf[consuming]->ready = FLAG_UNUSED; > + __atomic_store_n(&info->page_flag_buf[consuming]->ready, > + FLAG_UNUSED, __ATOMIC_SEQ_CST); > info->page_flag_buf[consuming] = > info->page_flag_buf[consuming]->next; > } > finish:
