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server: fix potential races on deallocation

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This commit is contained in:
Thomas Schoebel-Theuer 2022-05-31 21:51:21 +02:00
parent 3434096fcf
commit acf7d0c4cc
2 changed files with 56 additions and 16 deletions
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68
kernel/mars_server.c
View File

@ -167,10 +167,6 @@ int cb_thread(void *data)
mars_shutdown_socket(sock);
}
if (mref_a->data) {
brick_block_free(mref_a->data, mref_a->len);
mref->ref_data = NULL;
}
if (mref_a->do_put) {
GENERIC_INPUT_CALL_VOID(brick->inputs[0], mref_put, mref);
atomic_dec(&brick->in_flight);
@ -246,16 +242,18 @@ int server_io(struct server_brick *brick, struct mars_socket *sock, struct mars_
goto done;
}
mref_a->brick = brick;
mref_a->data = mref->ref_data;
mref_a->first_data = mref->ref_data;
status = mars_recv_mref(sock, mref, cmd);
if (status < 0) {
mars_free_mref(mref);
goto done;
}
mref_a->data = mref->ref_data;
mref_a->len = mref->ref_len;
if (!mref_a->first_data) {
mref_a->first_data = mref->ref_data;
mref_a->first_len = mref->ref_len;
}
SETUP_CALLBACK(mref, server_endio, mref_a);
amount = 0;
@ -270,10 +268,13 @@ int server_io(struct server_brick *brick, struct mars_socket *sock, struct mars_
status = 0; // continue serving requests
goto done;
}
mref_a->data = mref->ref_data;
mref_a->len = mref->ref_len;
if (!mref_a->first_data) {
mref_a->first_data = mref->ref_data;
mref_a->first_len = mref->ref_len;
}
mref_a->do_put = true;
atomic_inc(&brick->in_flight);
GENERIC_INPUT_CALL_VOID(brick->inputs[0], mref_io, mref);
done:
@ -798,15 +799,54 @@ void server_reset_statistics(struct server_brick *brick)
static int server_mref_aspect_init_fn(struct generic_aspect *_ini)
{
struct server_mref_aspect *ini = (void*)_ini;
INIT_LIST_HEAD(&ini->cb_head);
struct server_mref_aspect *mref_a = (void *)_ini;
INIT_LIST_HEAD(&mref_a->cb_head);
return 0;
}
/* This is responsible for _safe_ transition to deallocate state.
*/
static void server_mref_aspect_exit_fn(struct generic_aspect *_ini)
{
struct server_mref_aspect *ini = (void*)_ini;
CHECK_HEAD_EMPTY(&ini->cb_head);
struct server_mref_aspect *mref_a = (void *)_ini;
void *first_data;
int first_len;
/* For safety, do not leave dangling pointers.
* We don't want to win any micro-benchmarks here.
* We need to ensure geo-redundancy over long distances.
* When unsure, test via poisoning, independently at page
* granularity and at brick / object / aspect level.
*/
first_data = mref_a->first_data;
first_len = mref_a->first_len;
if (first_data && first_len) {
struct mref_object *mref = mref_a->object;
mref_a->first_data = NULL;
/* Prevent double free.
* Some callee might have allocated, and already freed
* via mref_data. This might have happened upon another
* thread / interrupt / callback / etc.
* Network transports / compression / etc may introduce
* further parallelism, independently from all of this.
* Be sure to deallocate the original address, since
* some address arithmetic might have happened
* somewhere else (e.g. sector-wise / packet fragments / etc).
* All of this might have happened below your ass,
* where you cannot see it, because we cannot know which
* which other (future) brick instances we are / were
* (re)connected during our unknown brick lifetime
* (which might range from milliseconds to months).
*/
if (mref && mref->ref_data) {
mref->ref_data = NULL;
brick_block_free(first_data, first_len);
}
}
CHECK_HEAD_EMPTY(&mref_a->cb_head);
}
MARS_MAKE_STATICS(server);

4
kernel/mars_server.h
View File

@ -42,8 +42,8 @@ struct server_mref_aspect {
GENERIC_ASPECT(mref);
struct server_brick *brick;
struct list_head cb_head;
void *data;
int len;
void *first_data;
int first_len;
bool do_put;
};