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authorSimo Sorce <simo@redhat.com>2012-12-11 17:23:19 -0500
committerJakub Hrozek <jhrozek@redhat.com>2012-12-13 20:43:12 +0100
commita5ccff776edfa776b8846f62a161aaf358e17b66 (patch)
tree850fbb5199323c380b4ef313c7432c6f5842c826 /src
parent3cf417b8502f5af34e6680f12a3365bcdd9fa40d (diff)
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Add a macro to copy with barriers
We have 2 places where we memcpy memory and need barriers protection. Use a macro so we can consolidate code in one place. Second fix for: https://fedorahosted.org/sssd/ticket/1694
Diffstat (limited to 'src')
-rw-r--r--src/sss_client/nss_mc_common.c47
1 files changed, 30 insertions, 17 deletions
diff --git a/src/sss_client/nss_mc_common.c b/src/sss_client/nss_mc_common.c
index a361f57b..59f5b257 100644
--- a/src/sss_client/nss_mc_common.c
+++ b/src/sss_client/nss_mc_common.c
@@ -38,18 +38,33 @@
/* FIXME: handle name upper/lower casing ? Maybe a flag passed down by
* sssd or a flag in sss_mc_header ? per domain ? */
+#define MEMCPY_WITH_BARRIERS(res, dest, src, len) \
+do { \
+ uint32_t _b1; \
+ res = false; \
+ _b1 = (src)->b1; \
+ if (MC_VALID_BARRIER(_b1)) { \
+ __sync_synchronize(); \
+ memcpy(dest, src, len); \
+ __sync_synchronize(); \
+ if ((src)->b2 == _b1) { \
+ res = true; \
+ } \
+ } \
+} while(0)
+
errno_t sss_nss_check_header(struct sss_cli_mc_ctx *ctx)
{
struct sss_mc_header h;
+ bool copy_ok;
int count;
/* retry barrier protected reading max 5 times then give up */
for (count = 5; count > 0; count--) {
- memcpy(&h, ctx->mmap_base, sizeof(struct sss_mc_header));
- /* we need a barrier here to make sure the compiler does not optimize
- * too much and avoids updating the register for the next check */
- __sync_synchronize();
- if (MC_VALID_BARRIER(h.b1) && h.b1 == h.b2) {
+ MEMCPY_WITH_BARRIERS(copy_ok, &h,
+ (struct sss_mc_header *)ctx->mmap_base,
+ sizeof(struct sss_mc_header));
+ if (copy_ok) {
/* record is consistent so we can proceed */
break;
}
@@ -181,11 +196,12 @@ errno_t sss_nss_mc_get_record(struct sss_cli_mc_ctx *ctx,
uint32_t slot, struct sss_mc_rec **_rec)
{
struct sss_mc_rec *rec;
- void *rec_buf = NULL;
+ struct sss_mc_rec *copy_rec = NULL;
size_t buf_size = 0;
size_t rec_len;
uint32_t b1;
uint32_t b2;
+ bool copy_ok;
int count;
int ret;
@@ -198,16 +214,16 @@ errno_t sss_nss_mc_get_record(struct sss_cli_mc_ctx *ctx,
__sync_synchronize();
rec_len = rec->len;
__sync_synchronize();
- b2 = rec->b1;
+ b2 = rec->b2;
if (!MC_VALID_BARRIER(b1) || b1 != b2) {
/* record is inconsistent, retry */
continue;
}
if (rec_len > buf_size) {
- free(rec_buf);
- rec_buf = malloc(rec_len);
- if (!rec_buf) {
+ free(copy_rec);
+ copy_rec = malloc(rec_len);
+ if (!copy_rec) {
ret = ENOMEM;
goto done;
}
@@ -215,13 +231,10 @@ errno_t sss_nss_mc_get_record(struct sss_cli_mc_ctx *ctx,
}
/* we cannot access data directly, we must copy data and then
* access the copy */
- memcpy(rec_buf, rec, rec_len);
- rec = (struct sss_mc_rec *)rec_buf;
+ MEMCPY_WITH_BARRIERS(copy_ok, copy_rec, rec, rec_len);
/* we must check data is consistent again after the copy */
- if (MC_VALID_BARRIER(rec->b1) &&
- rec->b1 == rec->b2 &&
- rec->len == rec_len) {
+ if (copy_ok && b1 == copy_rec->b2) {
/* record is consistent, use it */
break;
}
@@ -232,12 +245,12 @@ errno_t sss_nss_mc_get_record(struct sss_cli_mc_ctx *ctx,
goto done;
}
- *_rec = rec;
+ *_rec = copy_rec;
ret = 0;
done:
if (ret) {
- free(rec_buf);
+ free(copy_rec);
*_rec = NULL;
}
return ret;