I do not believe it's reorganizing code. I think the code in the first
section is wrong, and the second version is needed.
Once you've dec'd the refcount, you cannot access the pointer. At that
point, another thread could deref and free, and you'd be left with freed
memory. You *must* store that value in a local variable.
Daniel
On 08/03/2017 02:13 AM, William Allen Simpson wrote:
It's improperly reorganizing code.
===
Accessing freed memory at ==>
Logically, this couldn't happen!
int free_nfs_request(request_data_t *reqdata)
{
atomic_dec_uint32_t(&reqdata->r_d_refs);
LogDebug(COMPONENT_DISPATCH,
"%s: %p fd %d xp_refs %" PRIu32 " r_d_refs %" PRIu32,
__func__,
reqdata->r_u.req.svc.rq_xprt,
reqdata->r_u.req.svc.rq_xprt->xp_fd,
reqdata->r_u.req.svc.rq_xprt->xp_refs,
reqdata->r_d_refs);
if (reqdata->r_d_refs)
==> return reqdata->r_d_refs;
switch (reqdata->rtype) {
case NFS_REQUEST:
/* dispose RPC header */
if (reqdata->r_u.req.svc.rq_auth)
SVCAUTH_RELEASE(&(reqdata->r_u.req.svc));
XDR_DESTROY(reqdata->r_u.req.svc.rq_xdrs);
break;
default:
break;
}
SVC_RELEASE(reqdata->r_u.req.svc.rq_xprt, SVC_RELEASE_FLAG_NONE);
pool_free(request_pool, reqdata);
return 0;
}
===
This works by using local variables. Kinda pointlessly, when not
running log debug.
int free_nfs_request(request_data_t *reqdata)
{
SVCXPRT *xprt = reqdata->r_u.req.svc.rq_xprt;
uint32_t refs = atomic_dec_uint32_t(&reqdata->r_d_refs);
LogDebug(COMPONENT_DISPATCH,
"%s: %p fd %d xp_refs %" PRIu32 " r_d_refs %" PRIu32,
__func__,
xprt, xprt->xp_fd, xprt->xp_refs,
refs);
if (refs)
return refs;
switch (reqdata->rtype) {
case NFS_REQUEST:
/* dispose RPC header */
if (reqdata->r_u.req.svc.rq_auth)
SVCAUTH_RELEASE(&(reqdata->r_u.req.svc));
XDR_DESTROY(reqdata->r_u.req.svc.rq_xdrs);
break;
default:
break;
}
SVC_RELEASE(xprt, SVC_RELEASE_FLAG_NONE);
pool_free(request_pool, reqdata);
return 0;
}
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