From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 118f457da9ed58a79e24b73c2ef0aa1987241f0e ]
In the previous GC implementation, the shape of the inflight socket graph was not expected to change while GC was in progress.
MSG_PEEK was tricky because it could install inflight fd silently and transform the graph.
Let's say we peeked a fd, which was a listening socket, and accept()ed some embryo sockets from it. The garbage collection algorithm would have been confused because the set of sockets visited in scan_inflight() would change within the same GC invocation.
That's why we placed spin_lock(&unix_gc_lock) and spin_unlock() in unix_peek_fds() with a fat comment.
In the new GC implementation, we no longer garbage-collect the socket if it exists in another queue, that is, if it has a bridge to another SCC. Also, accept() will require the lock if it has edges.
Thus, we need not do the complicated lock dance.
Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Link: https://lore.kernel.org/r/20240401173125.92184-3-kuniyu@amazon.com Signed-off-by: Jakub Kicinski kuba@kernel.org (cherry picked from commit 118f457da9ed58a79e24b73c2ef0aa1987241f0e) Signed-off-by: Lee Jones lee@kernel.org --- include/net/af_unix.h | 1 - net/unix/af_unix.c | 42 ------------------------------------------ net/unix/garbage.c | 2 +- 3 files changed, 1 insertion(+), 44 deletions(-)
diff --git a/include/net/af_unix.h b/include/net/af_unix.h index d88ca51a9081d..47042de4a2a9c 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -17,7 +17,6 @@ static inline struct unix_sock *unix_get_socket(struct file *filp) } #endif
-extern spinlock_t unix_gc_lock; extern unsigned int unix_tot_inflight; void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver); void unix_del_edges(struct scm_fp_list *fpl); diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index eee0bccd7877b..df70d8a7ee837 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1796,48 +1796,6 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb) static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb) { scm->fp = scm_fp_dup(UNIXCB(skb).fp); - - /* - * Garbage collection of unix sockets starts by selecting a set of - * candidate sockets which have reference only from being in flight - * (total_refs == inflight_refs). This condition is checked once during - * the candidate collection phase, and candidates are marked as such, so - * that non-candidates can later be ignored. While inflight_refs is - * protected by unix_gc_lock, total_refs (file count) is not, hence this - * is an instantaneous decision. - * - * Once a candidate, however, the socket must not be reinstalled into a - * file descriptor while the garbage collection is in progress. - * - * If the above conditions are met, then the directed graph of - * candidates (*) does not change while unix_gc_lock is held. - * - * Any operations that changes the file count through file descriptors - * (dup, close, sendmsg) does not change the graph since candidates are - * not installed in fds. - * - * Dequeing a candidate via recvmsg would install it into an fd, but - * that takes unix_gc_lock to decrement the inflight count, so it's - * serialized with garbage collection. - * - * MSG_PEEK is special in that it does not change the inflight count, - * yet does install the socket into an fd. The following lock/unlock - * pair is to ensure serialization with garbage collection. It must be - * done between incrementing the file count and installing the file into - * an fd. - * - * If garbage collection starts after the barrier provided by the - * lock/unlock, then it will see the elevated refcount and not mark this - * as a candidate. If a garbage collection is already in progress - * before the file count was incremented, then the lock/unlock pair will - * ensure that garbage collection is finished before progressing to - * installing the fd. - * - * (*) A -> B where B is on the queue of A or B is on the queue of C - * which is on the queue of listening socket A. - */ - spin_lock(&unix_gc_lock); - spin_unlock(&unix_gc_lock); }
static void unix_destruct_scm(struct sk_buff *skb) diff --git a/net/unix/garbage.c b/net/unix/garbage.c index 89ea71d9297ba..12a4ec27e0d4d 100644 --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -183,7 +183,7 @@ static void unix_free_vertices(struct scm_fp_list *fpl) } }
-DEFINE_SPINLOCK(unix_gc_lock); +static DEFINE_SPINLOCK(unix_gc_lock); unsigned int unix_tot_inflight;
void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver)