Cc: Paolo for preexisting issues due to commit 1e356fc14be.
Fei Li <address@hidden> writes:
From: Fei Li <address@hidden>
Supplement the error handling for touch_all_pages: add an Error
parameter for it to propagate the error to its caller to do the
handling in case it fails.
Cc: Markus Armbruster <address@hidden>
Signed-off-by: Fei Li <address@hidden>
---
util/oslib-posix.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index b6c2ee270d..b4dd3d8970 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
Some context we'll need below:
static void sigbus_handler(int signal)
{
int i;
if (memset_thread) {
for (i = 0; i < memset_num_threads; i++) {
if (qemu_thread_is_self(&memset_thread[i].pgthread)) {
siglongjmp(memset_thread[i].env, 1);
}
}
}
}
Preexisting, not this patch's business: touch_all_pages() sets
@memset_num_threads to the number of desired threads, then leisurely
populates memset_thread[], starting threads as it goes. If one of these
threads catches SIGBUS before memset_thread[] is completely populated,
memset_thread[i].pgthread can be null here. qemu_thread_is_self()
dereferences it. Oops.
Note there's a time window between qemu_thread_create() starting the
thread and storing it in memset_thread[i].pgthread. Any fix will have
to work even when the thread catches SIGBUS within that time window.
static void *do_touch_pages(void *arg)
{
MemsetThread *memset_args = (MemsetThread *)arg;
sigset_t set, oldset;
/* unblock SIGBUS */
sigemptyset(&set);
sigaddset(&set, SIGBUS);
pthread_sigmask(SIG_UNBLOCK, &set, &oldset);
if (sigsetjmp(memset_args->env, 1)) {
memset_thread_failed = true;
} else {
[...]
}
pthread_sigmask(SIG_SETMASK, &oldset, NULL);
return NULL;
}
We set @memset_thread_failed on SIGBUS in a memset thread.
@@ -435,7 +435,7 @@ static inline int get_memset_num_threads(int smp_cpus)
}
static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
- int smp_cpus)
+ int smp_cpus, Error **errp)
{
size_t numpages_per_thread;
size_t size_per_thread;
char *addr = area;
int i = 0;
memset_thread_failed = false;
We clear @memset_thread_failed before we create the memset threads.
Preexisting, not this patch's business: use of global state without
synchronization leaves touch_all_pages() and thus os_mem_prealloc() not
thread-safe. Even when that's just fine, it warrants at least a big fat
comment, and ideally assertions to catch misuse.
memset_num_threads = get_memset_num_threads(smp_cpus);
memset_thread = g_new0(MemsetThread, memset_num_threads);
numpages_per_thread = (numpages / memset_num_threads);
size_per_thread = (hpagesize * numpages_per_thread);
for (i = 0; i < memset_num_threads; i++) {
memset_thread[i].addr = addr;
@@ -452,20 +452,29 @@ static bool touch_all_pages(char *area, size_t hpagesize,
size_t numpages,
memset_thread[i].numpages = (i == (memset_num_threads - 1)) ?
numpages : numpages_per_thread;
memset_thread[i].hpagesize = hpagesize;
- /* TODO: let the callers handle the error instead of abort() here */
- qemu_thread_create(&memset_thread[i].pgthread, "touch_pages",
- do_touch_pages, &memset_thread[i],
- QEMU_THREAD_JOINABLE, &error_abort);
+ if (qemu_thread_create(&memset_thread[i].pgthread, "touch_pages",
+ do_touch_pages, &memset_thread[i],
+ QEMU_THREAD_JOINABLE, errp) < 0) {
+ memset_thread_failed = true;
We set @memset_thread_failed when creating a memset thread fails. @errp
contains an error then.
+ break;
+ }
addr += size_per_thread;
numpages -= numpages_per_thread;
}
+
+ memset_num_threads = i;
for (i = 0; i < memset_num_threads; i++) {
qemu_thread_join(&memset_thread[i].pgthread);
}
g_free(memset_thread);
memset_thread = NULL;
- return memset_thread_failed;
+ if (memset_thread_failed) {
+ error_append_hint(errp, "os_mem_prealloc: Insufficient free host "
+ "memory pages available to allocate guest RAM");
+ return false;
@memset_thread_failed is true when creating a memset thread failed, or a
memset thread caught SIGBUS.
@errp contains an error only if the former is the case.
If we succeeded in creating all threads, but got SIGBUS, @errp is null,
and error_append_hint() does nothing. touch_all_pages() then fails
without setting an error.
Suggested fix: drop the memset_thread_failed = true on thread creation
failure, and do something like
for (j = 0; j < i; j++) {
qemu_thread_join(&memset_thread[i].pgthread);
void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
@@ -488,10 +497,7 @@ void os_mem_prealloc(int fd, char *area, size_t memory,
int smp_cpus,
}
/* touch pages simultaneously */
- if (touch_all_pages(area, hpagesize, numpages, smp_cpus)) {
- error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
- "pages available to allocate guest RAM");
- }
+ touch_all_pages(area, hpagesize, numpages, smp_cpus, errp);
ret = sigaction(SIGBUS, &oldact, NULL);
if (ret) {