This patch makes pipes use the pipe pair lock instead of the kernel lock
for pipe klist serialization.
In pipe_kqfilter(), the pipe pair lock is already held, so it is
appropriate to keep on using klist_insert_locked() there.
filt_pipedetach(), on the other hand, can be shortened by using
klist_remove(). klist_remove() acquires the pipe pair lock internally.
Note that the pipe pair lock has to be held when calling KNOTE() with
a pipe klist as the argument. pipeselwakeup() calls KNOTE() directly
as well as indirectly through selwakeup().
There is a quirk in how pipe knotes are attached. Read filter knotes
attach to the pipe end at hand, whereas write filter knotes attach to the
other end of the pipe. As a consequence, when a pipe end has already been
closed, the klist can still contain knotes. This is why the klist_free()
calls are done only when the whole pair is destroyed.
OK?
Index: kern/sys_pipe.c
===================================================================
RCS file: src/sys/kern/sys_pipe.c,v
retrieving revision 1.125
diff -u -p -r1.125 sys_pipe.c
--- kern/sys_pipe.c 25 Dec 2020 12:59:52 -0000 1.125
+++ kern/sys_pipe.c 25 Dec 2020 15:10:05 -0000
@@ -126,6 +126,7 @@ void pipe_iounlock(struct pipe *);
int pipe_iosleep(struct pipe *, const char *);
struct pipe_pair *pipe_pair_create(void);
+void pipe_pair_destroy(struct pipe_pair *);
/*
* The pipe system call for the DTYPE_PIPE type of pipes
@@ -853,8 +854,7 @@ pipe_destroy(struct pipe *cpipe)
rw_exit_write(cpipe->pipe_lock);
if (ppipe == NULL)
- pool_put(&pipe_pair_pool, cpipe->pipe_pair);
+ pipe_pair_destroy(cpipe->pipe_pair);
}
/*
@@ -913,9 +914,7 @@ filt_pipedetach(struct knote *kn)
{
struct pipe *cpipe = kn->kn_hook;
- rw_enter_write(cpipe->pipe_lock);
- klist_remove_locked(&cpipe->pipe_sel.si_note, kn);
- rw_exit_write(cpipe->pipe_lock);
+ klist_remove(&cpipe->pipe_sel.si_note, kn);
}
int
@@ -997,6 +996,9 @@ pipe_pair_create(void)
pp->pp_wpipe.pipe_lock = &pp->pp_lock;
pp->pp_rpipe.pipe_lock = &pp->pp_lock;
+ klist_init_rwlock(&pp->pp_wpipe.pipe_sel.si_note, &pp->pp_lock);
+ klist_init_rwlock(&pp->pp_rpipe.pipe_sel.si_note, &pp->pp_lock);
+
if (pipe_create(&pp->pp_wpipe) || pipe_create(&pp->pp_rpipe))
goto err;
return (pp);
@@ -1005,3 +1007,11 @@ err:
pipe_destroy(&pp->pp_rpipe);
return (NULL);
}
+
+void
+pipe_pair_destroy(struct pipe_pair *pp)
+{
+ klist_free(&pp->pp_wpipe.pipe_sel.si_note);
+ klist_free(&pp->pp_rpipe.pipe_sel.si_note);
+ pool_put(&pipe_pair_pool, pp);
+}
