Make it possible to run pipe(2) and pipe2(2) mostly w/o KERNEL_LOCK():

- Update counters atomatically
- Use IPL_MPFLOOR for pipe's pool.
- Grab the KERNEL_LOCK() before calling km_alloc(9) & km_free(9)

Inputs from kettenis@, ok visa@

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index f3cf0fa..d9c68a3 100644 (file)
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: sys_pipe.c,v 1.82 2018/07/10 08:58:50 mpi Exp $       */
+/*     $OpenBSD: sys_pipe.c,v 1.83 2018/08/13 14:35:29 mpi Exp $       */
 
 /*
  * Copyright (c) 1996 John S. Dyson
@@ -91,8 +91,8 @@ struct filterops pipe_wfiltops =
  * Limit the number of "big" pipes
  */
 #define LIMITBIGPIPES  32
-int nbigpipe;
-static int amountpipekva;
+unsigned int nbigpipe;
+static unsigned int amountpipekva;
 
 struct pool pipe_pool;
 
@@ -214,7 +214,9 @@ pipespace(struct pipe *cpipe, u_int size)
 {
        caddr_t buffer;
 
+       KERNEL_LOCK();
        buffer = km_alloc(size, &kv_any, &kp_pageable, &kd_waitok);
+       KERNEL_UNLOCK();
        if (buffer == NULL) {
                return (ENOMEM);
        }
@@ -227,7 +229,7 @@ pipespace(struct pipe *cpipe, u_int size)
        cpipe->pipe_buffer.out = 0;
        cpipe->pipe_buffer.cnt = 0;
 
-       amountpipekva += cpipe->pipe_buffer.size;
+       atomic_add_int(&amountpipekva, cpipe->pipe_buffer.size);
 
        return (0);
 }
@@ -444,15 +446,18 @@ pipe_write(struct file *fp, off_t *poff, struct uio *uio, struct ucred *cred)
         * so.
         */
        if ((uio->uio_resid > PIPE_SIZE) &&
-           (nbigpipe < LIMITBIGPIPES) &&
            (wpipe->pipe_buffer.size <= PIPE_SIZE) &&
            (wpipe->pipe_buffer.cnt == 0)) {
+               unsigned int npipe;
 
-               if ((error = pipelock(wpipe)) == 0) {
-                       if (pipespace(wpipe, BIG_PIPE_SIZE) == 0)
-                               nbigpipe++;
+               npipe = atomic_inc_int_nv(&nbigpipe);
+               if ((npipe <= LIMITBIGPIPES) &&
+                   (error = pipelock(wpipe)) == 0) {
+                       if (pipespace(wpipe, BIG_PIPE_SIZE) != 0)
+                               atomic_dec_int(&nbigpipe);
                        pipeunlock(wpipe);
-               }
+               } else
+                       atomic_dec_int(&nbigpipe);
        }
 
        /*
@@ -759,13 +764,16 @@ pipe_close(struct file *fp, struct proc *p)
 void
 pipe_free_kmem(struct pipe *cpipe)
 {
+       u_int size = cpipe->pipe_buffer.size;
+
        if (cpipe->pipe_buffer.buffer != NULL) {
-               if (cpipe->pipe_buffer.size > PIPE_SIZE)
-                       --nbigpipe;
-               amountpipekva -= cpipe->pipe_buffer.size;
-               km_free(cpipe->pipe_buffer.buffer, cpipe->pipe_buffer.size,
-                   &kv_any, &kp_pageable);
+               KERNEL_LOCK();
+               km_free(cpipe->pipe_buffer.buffer, size, &kv_any, &kp_pageable);
+               KERNEL_UNLOCK();
+               atomic_sub_int(&amountpipekva, size);
                cpipe->pipe_buffer.buffer = NULL;
+               if (size > PIPE_SIZE)
+                       atomic_dec_int(&nbigpipe);
        }
 }
 
@@ -777,7 +785,6 @@ pipeclose(struct pipe *cpipe)
 {
        struct pipe *ppipe;
        if (cpipe) {
-               
                pipeselwakeup(cpipe);
 
                /*
@@ -889,7 +896,7 @@ filt_pipewrite(struct knote *kn, long hint)
 void
 pipe_init(void)
 {
-       pool_init(&pipe_pool, sizeof(struct pipe), 0, IPL_NONE, PR_WAITOK,
+       pool_init(&pipe_pool, sizeof(struct pipe), 0, IPL_MPFLOOR, PR_WAITOK,
            "pipepl", NULL);
 }