fix idr_find() locking
This is a patch that fixes the way idr_find() used to be called in ipc_lock():
in all the paths that don't imply an update of the ipcs idr, it was called
without the idr tree being locked.
The changes are:
. in ipc_ids, the mutex has been changed into a reader/writer semaphore.
. ipc_lock() now takes the mutex as a reader during the idr_find().
. a new routine ipc_lock_down() has been defined: it doesn't take the
mutex, assuming that it is being held by the caller. This is the routine
that is now called in all the update paths.
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/shm.c b/ipc/shm.c
index f28f2a3..b27d31f 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -35,7 +35,7 @@
#include <linux/capability.h>
#include <linux/ptrace.h>
#include <linux/seq_file.h>
-#include <linux/mutex.h>
+#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/mount.h>
@@ -83,8 +83,8 @@
}
/*
- * Called with shm_ids.mutex and the shp structure locked.
- * Only shm_ids.mutex remains locked on exit.
+ * Called with shm_ids.rw_mutex (writer) and the shp structure locked.
+ * Only shm_ids.rw_mutex remains locked on exit.
*/
static void do_shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *shp)
{
@@ -115,7 +115,7 @@
int next_id;
int total, in_use;
- mutex_lock(&shm_ids(ns).mutex);
+ down_write(&shm_ids(ns).rw_mutex);
in_use = shm_ids(ns).in_use;
@@ -127,7 +127,7 @@
do_shm_rmid(ns, shp);
total++;
}
- mutex_unlock(&shm_ids(ns).mutex);
+ up_write(&shm_ids(ns).rw_mutex);
kfree(ns->ids[IPC_SHM_IDS]);
ns->ids[IPC_SHM_IDS] = NULL;
@@ -141,6 +141,31 @@
IPC_SHM_IDS, sysvipc_shm_proc_show);
}
+/*
+ * shm_lock_(check_)down routines are called in the paths where the rw_mutex
+ * is held to protect access to the idr tree.
+ */
+static inline struct shmid_kernel *shm_lock_down(struct ipc_namespace *ns,
+ int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_lock_down(&shm_ids(ns), id);
+
+ return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
+static inline struct shmid_kernel *shm_lock_check_down(
+ struct ipc_namespace *ns,
+ int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_lock_check_down(&shm_ids(ns), id);
+
+ return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
+/*
+ * shm_lock_(check_) routines are called in the paths where the rw_mutex
+ * is not held.
+ */
static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
{
struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
@@ -189,7 +214,7 @@
* @ns: namespace
* @shp: struct to free
*
- * It has to be called with shp and shm_ids.mutex locked,
+ * It has to be called with shp and shm_ids.rw_mutex (writer) locked,
* but returns with shp unlocked and freed.
*/
static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
@@ -220,9 +245,9 @@
struct shmid_kernel *shp;
struct ipc_namespace *ns = sfd->ns;
- mutex_lock(&shm_ids(ns).mutex);
+ down_write(&shm_ids(ns).rw_mutex);
/* remove from the list of attaches of the shm segment */
- shp = shm_lock(ns, sfd->id);
+ shp = shm_lock_down(ns, sfd->id);
BUG_ON(IS_ERR(shp));
shp->shm_lprid = task_tgid_vnr(current);
shp->shm_dtim = get_seconds();
@@ -232,7 +257,7 @@
shm_destroy(ns, shp);
else
shm_unlock(shp);
- mutex_unlock(&shm_ids(ns).mutex);
+ up_write(&shm_ids(ns).rw_mutex);
}
static int shm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
@@ -353,7 +378,7 @@
* @ns: namespace
* @params: ptr to the structure that contains key, size and shmflg
*
- * Called with shm_ids.mutex held
+ * Called with shm_ids.rw_mutex held as a writer.
*/
static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
@@ -442,7 +467,7 @@
}
/*
- * Called with shm_ids.mutex and ipcp locked.
+ * Called with shm_ids.rw_mutex and ipcp locked.
*/
static inline int shm_security(struct kern_ipc_perm *ipcp, int shmflg)
{
@@ -453,7 +478,7 @@
}
/*
- * Called with shm_ids.mutex and ipcp locked.
+ * Called with shm_ids.rw_mutex and ipcp locked.
*/
static inline int shm_more_checks(struct kern_ipc_perm *ipcp,
struct ipc_params *params)
@@ -578,7 +603,7 @@
}
/*
- * Called with shm_ids.mutex held
+ * Called with shm_ids.rw_mutex held as a reader
*/
static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
unsigned long *swp)
@@ -649,9 +674,9 @@
if(copy_shminfo_to_user (buf, &shminfo, version))
return -EFAULT;
- mutex_lock(&shm_ids(ns).mutex);
+ down_read(&shm_ids(ns).rw_mutex);
err = ipc_get_maxid(&shm_ids(ns));
- mutex_unlock(&shm_ids(ns).mutex);
+ up_read(&shm_ids(ns).rw_mutex);
if(err<0)
err = 0;
@@ -666,14 +691,14 @@
return err;
memset(&shm_info,0,sizeof(shm_info));
- mutex_lock(&shm_ids(ns).mutex);
+ down_read(&shm_ids(ns).rw_mutex);
shm_info.used_ids = shm_ids(ns).in_use;
shm_get_stat (ns, &shm_info.shm_rss, &shm_info.shm_swp);
shm_info.shm_tot = ns->shm_tot;
shm_info.swap_attempts = 0;
shm_info.swap_successes = 0;
err = ipc_get_maxid(&shm_ids(ns));
- mutex_unlock(&shm_ids(ns).mutex);
+ up_read(&shm_ids(ns).rw_mutex);
if(copy_to_user (buf, &shm_info, sizeof(shm_info))) {
err = -EFAULT;
goto out;
@@ -786,8 +811,8 @@
* Instead we set a destroyed flag, and then blow
* the name away when the usage hits zero.
*/
- mutex_lock(&shm_ids(ns).mutex);
- shp = shm_lock_check(ns, shmid);
+ down_write(&shm_ids(ns).rw_mutex);
+ shp = shm_lock_check_down(ns, shmid);
if (IS_ERR(shp)) {
err = PTR_ERR(shp);
goto out_up;
@@ -809,7 +834,7 @@
goto out_unlock_up;
do_shm_rmid(ns, shp);
- mutex_unlock(&shm_ids(ns).mutex);
+ up_write(&shm_ids(ns).rw_mutex);
goto out;
}
@@ -824,8 +849,8 @@
err = -EFAULT;
goto out;
}
- mutex_lock(&shm_ids(ns).mutex);
- shp = shm_lock_check(ns, shmid);
+ down_write(&shm_ids(ns).rw_mutex);
+ shp = shm_lock_check_down(ns, shmid);
if (IS_ERR(shp)) {
err = PTR_ERR(shp);
goto out_up;
@@ -864,7 +889,7 @@
out_unlock_up:
shm_unlock(shp);
out_up:
- mutex_unlock(&shm_ids(ns).mutex);
+ up_write(&shm_ids(ns).rw_mutex);
goto out;
out_unlock:
shm_unlock(shp);
@@ -998,8 +1023,8 @@
fput(file);
out_nattch:
- mutex_lock(&shm_ids(ns).mutex);
- shp = shm_lock(ns, shmid);
+ down_write(&shm_ids(ns).rw_mutex);
+ shp = shm_lock_down(ns, shmid);
BUG_ON(IS_ERR(shp));
shp->shm_nattch--;
if(shp->shm_nattch == 0 &&
@@ -1007,7 +1032,7 @@
shm_destroy(ns, shp);
else
shm_unlock(shp);
- mutex_unlock(&shm_ids(ns).mutex);
+ up_write(&shm_ids(ns).rw_mutex);
out:
return err;