6.6-stable review patch. If anyone has any objections, please let me know.
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From: Kuniyuki Iwashima kuniyu@amazon.com
commit 8b90a9f819dc2a06baae4ec1a64d875e53b824ec upstream.
If more than 16000 inflight AF_UNIX sockets exist and the garbage collector is not running, unix_(dgram|stream)_sendmsg() call unix_gc(). Also, they wait for unix_gc() to complete.
In unix_gc(), all inflight AF_UNIX sockets are traversed at least once, and more if they are the GC candidate. Thus, sendmsg() significantly slows down with too many inflight AF_UNIX sockets.
There is a small window to invoke multiple unix_gc() instances, which will then be blocked by the same spinlock except for one.
Let's convert unix_gc() to use struct work so that it will not consume CPUs unnecessarily.
Note WRITE_ONCE(gc_in_progress, true) is moved before running GC. If we leave the WRITE_ONCE() as is and use the following test to call flush_work(), a process might not call it.
CPU 0 CPU 1 --- --- start work and call __unix_gc() if (work_pending(&unix_gc_work) || <-- false READ_ONCE(gc_in_progress)) <-- false flush_work(); <-- missed! WRITE_ONCE(gc_in_progress, true)
Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Link: https://lore.kernel.org/r/20240123170856.41348-5-kuniyu@amazon.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/unix/garbage.c | 54 ++++++++++++++++++++++++++--------------------------- 1 file changed, 27 insertions(+), 27 deletions(-)
--- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -86,7 +86,6 @@ /* Internal data structures and random procedures: */
static LIST_HEAD(gc_candidates); -static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *), struct sk_buff_head *hitlist) @@ -182,23 +181,8 @@ static void inc_inflight_move_tail(struc }
static bool gc_in_progress; -#define UNIX_INFLIGHT_TRIGGER_GC 16000 - -void wait_for_unix_gc(void) -{ - /* If number of inflight sockets is insane, - * force a garbage collect right now. - * Paired with the WRITE_ONCE() in unix_inflight(), - * unix_notinflight() and gc_in_progress(). - */ - if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC && - !READ_ONCE(gc_in_progress)) - unix_gc(); - wait_event(unix_gc_wait, !READ_ONCE(gc_in_progress)); -}
-/* The external entry point: unix_gc() */ -void unix_gc(void) +static void __unix_gc(struct work_struct *work) { struct sk_buff *next_skb, *skb; struct unix_sock *u; @@ -209,13 +193,6 @@ void unix_gc(void)
spin_lock(&unix_gc_lock);
- /* Avoid a recursive GC. */ - if (gc_in_progress) - goto out; - - /* Paired with READ_ONCE() in wait_for_unix_gc(). */ - WRITE_ONCE(gc_in_progress, true); - /* First, select candidates for garbage collection. Only * in-flight sockets are considered, and from those only ones * which don't have any external reference. @@ -346,8 +323,31 @@ void unix_gc(void) /* Paired with READ_ONCE() in wait_for_unix_gc(). */ WRITE_ONCE(gc_in_progress, false);
- wake_up(&unix_gc_wait); - - out: spin_unlock(&unix_gc_lock); } + +static DECLARE_WORK(unix_gc_work, __unix_gc); + +void unix_gc(void) +{ + WRITE_ONCE(gc_in_progress, true); + queue_work(system_unbound_wq, &unix_gc_work); +} + +#define UNIX_INFLIGHT_TRIGGER_GC 16000 + +void wait_for_unix_gc(void) +{ + /* If number of inflight sockets is insane, + * force a garbage collect right now. + * + * Paired with the WRITE_ONCE() in unix_inflight(), + * unix_notinflight(), and __unix_gc(). + */ + if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC && + !READ_ONCE(gc_in_progress)) + unix_gc(); + + if (READ_ONCE(gc_in_progress)) + flush_work(&unix_gc_work); +}