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Subject[PATCH] ipc 1/3: Add refcount to ipc_rcu_alloc
Hi,

the lifetime of the ipc objects (sem array, msg queue, shm mapping) is
controlled by kern_ipc_perms->lock - a spinlock. There is no simple way
to reacquire this spinlock after it was dropped to
schedule()/kmalloc/copy_{to,from}_user/whatever.

The attached patch adds a reference count as a preparation to get rid of
sem_revalidate().

Andrew, could you add it to -mm?

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>

diff -u 2.6/ipc/msg.c build-2.6/ipc/msg.c
--- 2.6/ipc/msg.c 2004-07-03 19:08:47.273962648 +0200
+++ build-2.6/ipc/msg.c 2004-07-03 19:16:03.445654472 +0200
@@ -100,14 +100,14 @@
msq->q_perm.security = NULL;
retval = security_msg_queue_alloc(msq);
if (retval) {
- ipc_rcu_free(msq, sizeof(*msq));
+ ipc_rcu_putref(msq);
return retval;
}

id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
if(id == -1) {
security_msg_queue_free(msq);
- ipc_rcu_free(msq, sizeof(*msq));
+ ipc_rcu_putref(msq);
return -ENOSPC;
}

@@ -193,7 +193,7 @@
}
atomic_sub(msq->q_cbytes, &msg_bytes);
security_msg_queue_free(msq);
- ipc_rcu_free(msq, sizeof(struct msg_queue));
+ ipc_rcu_putref(msq);
}

asmlinkage long sys_msgget (key_t key, int msgflg)
diff -u 2.6/ipc/sem.c build-2.6/ipc/sem.c
--- 2.6/ipc/sem.c 2004-07-03 19:08:47.274962496 +0200
+++ build-2.6/ipc/sem.c 2004-07-03 19:16:08.845833520 +0200
@@ -179,14 +179,14 @@
sma->sem_perm.security = NULL;
retval = security_sem_alloc(sma);
if (retval) {
- ipc_rcu_free(sma, size);
+ ipc_rcu_putref(sma);
return retval;
}

id = ipc_addid(&sem_ids, &sma->sem_perm, sc_semmni);
if(id == -1) {
security_sem_free(sma);
- ipc_rcu_free(sma, size);
+ ipc_rcu_putref(sma);
return -ENOSPC;
}
used_sems += nsems;
@@ -473,7 +473,7 @@
used_sems -= sma->sem_nsems;
size = sizeof (*sma) + sma->sem_nsems * sizeof (struct sem);
security_sem_free(sma);
- ipc_rcu_free(sma, size);
+ ipc_rcu_putref(sma);
}

static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
diff -u 2.6/ipc/shm.c build-2.6/ipc/shm.c
--- 2.6/ipc/shm.c 2004-07-03 19:08:47.281961432 +0200
+++ build-2.6/ipc/shm.c 2004-07-03 19:09:16.646497344 +0200
@@ -117,7 +117,7 @@
shmem_lock(shp->shm_file, 0);
fput (shp->shm_file);
security_shm_free(shp);
- ipc_rcu_free(shp, sizeof(struct shmid_kernel));
+ ipc_rcu_putref(shp);
}

/*
@@ -194,7 +194,7 @@
shp->shm_perm.security = NULL;
error = security_shm_alloc(shp);
if (error) {
- ipc_rcu_free(shp, sizeof(*shp));
+ ipc_rcu_putref(shp);
return error;
}

@@ -234,7 +234,7 @@
fput(file);
no_file:
security_shm_free(shp);
- ipc_rcu_free(shp, sizeof(*shp));
+ ipc_rcu_putref(shp);
return error;
}

diff -u 2.6/ipc/util.c build-2.6/ipc/util.c
--- 2.6/ipc/util.c 2004-07-03 19:08:47.286960672 +0200
+++ build-2.6/ipc/util.c 2004-07-03 19:20:00.162668016 +0200
@@ -135,7 +135,6 @@
new[i].p = NULL;
}
old = ids->entries;
- i = ids->size;

/*
* before setting the ids->entries to the new array, there must be a
@@ -147,7 +146,7 @@
smp_wmb(); /* prevent indexing into old array based on new size. */
ids->size = newsize;

- ipc_rcu_free(old, sizeof(struct ipc_id)*i);
+ ipc_rcu_putref(old);
return ids->size;
}

@@ -292,10 +291,21 @@
void *data[0];
};

+struct ipc_rcu_hdr
+{
+ int refcount;
+ int is_vmalloc;
+};
+
+#define HDRLEN_KMALLOC (sizeof(struct ipc_rcu_kmalloc) > sizeof(struct ipc_rcu_hdr) ? \
+ sizeof(struct ipc_rcu_kmalloc) : sizeof(struct ipc_rcu_hdr))
+#define HDRLEN_VMALLOC (sizeof(struct ipc_rcu_vmalloc) > sizeof(struct ipc_rcu_hdr) ? \
+ sizeof(struct ipc_rcu_vmalloc) : sizeof(struct ipc_rcu_hdr))
+
static inline int rcu_use_vmalloc(int size)
{
/* Too big for a single page? */
- if (sizeof(struct ipc_rcu_kmalloc) + size > PAGE_SIZE)
+ if (HDRLEN_KMALLOC + size > PAGE_SIZE)
return 1;
return 0;
}
@@ -317,16 +327,29 @@
* workqueue if necessary (for vmalloc).
*/
if (rcu_use_vmalloc(size)) {
- out = vmalloc(sizeof(struct ipc_rcu_vmalloc) + size);
- if (out) out += sizeof(struct ipc_rcu_vmalloc);
+ out = vmalloc(HDRLEN_VMALLOC + size);
+ if (out) {
+ out += HDRLEN_VMALLOC;
+ ((struct ipc_rcu_hdr *)out)[-1].is_vmalloc = 1;
+ ((struct ipc_rcu_hdr *)out)[-1].refcount = 1;
+ }
} else {
- out = kmalloc(sizeof(struct ipc_rcu_kmalloc)+size, GFP_KERNEL);
- if (out) out += sizeof(struct ipc_rcu_kmalloc);
+ out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
+ if (out) {
+ out += HDRLEN_KMALLOC;
+ ((struct ipc_rcu_hdr *)out)[-1].is_vmalloc = 0;
+ ((struct ipc_rcu_hdr *)out)[-1].refcount = 1;
+ }
}

return out;
}

+void ipc_rcu_getref(void *ptr)
+{
+ ((struct ipc_rcu_hdr *)ptr)[-1].refcount++;
+}
+
/**
* ipc_schedule_free - free ipc + rcu space
*
@@ -355,11 +378,12 @@
kfree(free);
}

-
-
-void ipc_rcu_free(void* ptr, int size)
+void ipc_rcu_putref(void *ptr)
{
- if (rcu_use_vmalloc(size)) {
+ if (--((struct ipc_rcu_hdr *)ptr)[-1].refcount > 0)
+ return;
+
+ if (((struct ipc_rcu_hdr *)ptr)[-1].is_vmalloc) {
struct ipc_rcu_vmalloc *free;
free = ptr - sizeof(*free);
call_rcu(&free->rcu, ipc_schedule_free);
@@ -368,7 +392,6 @@
free = ptr - sizeof(*free);
call_rcu(&free->rcu, ipc_immediate_free);
}
-
}

/**
@@ -506,6 +529,12 @@
return out;
}

+void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
+{
+ rcu_read_lock();
+ spin_lock(&perm->lock);
+}
+
void ipc_unlock(struct kern_ipc_perm* perm)
{
spin_unlock(&perm->lock);
diff -u 2.6/ipc/util.h build-2.6/ipc/util.h
--- 2.6/ipc/util.h 2004-07-03 19:08:47.287960520 +0200
+++ build-2.6/ipc/util.h 2004-07-03 19:09:16.647497192 +0200
@@ -45,14 +45,20 @@
*/
void* ipc_alloc(int size);
void ipc_free(void* ptr, int size);
-/* for allocation that need to be freed by RCU
- * both function can sleep
+
+/*
+ * For allocation that need to be freed by RCU.
+ * Objects are reference counted, they start with reference count 1.
+ * getref increases the refcount, the putref call that reduces the recount
+ * to 0 schedules the rcu destruction. Caller must guarantee locking.
*/
void* ipc_rcu_alloc(int size);
-void ipc_rcu_free(void* arg, int size);
+void ipc_rcu_getref(void *ptr);
+void ipc_rcu_putref(void *ptr);

struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id);
struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id);
+void ipc_lock_by_ptr(struct kern_ipc_perm *ipcp);
void ipc_unlock(struct kern_ipc_perm* perm);
int ipc_buildid(struct ipc_ids* ids, int id, int seq);
int ipc_checkid(struct ipc_ids* ids, struct kern_ipc_perm* ipcp, int uid);
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