3.16.60-rc1 review patch. If anyone has any objections, please let me know.
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From: "Eric W. Biederman" ebiederm@xmission.com
commit 98f929b1bd4d0b7c7a77d0d9776d1b924db2e454 upstream.
Today shm_cpid and shm_lpid are remembered in the pid namespace of the creator and the processes that last touched a sysvipc shared memory segment. If you have processes in multiple pid namespaces that is just wrong, and I don't know how this has been over-looked for so long.
As only creation and shared memory attach and shared memory detach update the pids I do not expect there to be a repeat of the issues when struct pid was attached to each af_unix skb, which in some notable cases cut the performance in half. The problem was threads of the same process updating same struct pid from different cpus causing the cache line to be highly contended and bounce between cpus.
As creation, attach, and detach are expected to be rare operations for sysvipc shared memory segments I do not expect that kind of cache line ping pong to cause probems. In addition because the pid is at a fixed location in the structure instead of being dynamic on a skb, the reference count of the pid does not need to be updated on each operation if the pid is the same. This ability to simply skip the pid reference count changes if the pid is unchanging further reduces the likelihood of the a cache line holding a pid reference count ping-ponging between cpus.
Fixes: b488893a390e ("pid namespaces: changes to show virtual ids to user") Reviewed-by: Nagarathnam Muthusamy nagarathnam.muthusamy@oracle.com Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com [bwh: Backported to 3.16: adjust filename, context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/include/linux/shm.h +++ b/include/linux/shm.h @@ -14,8 +14,8 @@ struct shmid_kernel /* private to the ke time_t shm_atim; time_t shm_dtim; time_t shm_ctim; - pid_t shm_cprid; - pid_t shm_lprid; + struct pid *shm_cprid; + struct pid *shm_lprid; struct user_struct *mlock_user;
/* The task created the shm object. NULL if the task is dead. */ --- a/ipc/shm.c +++ b/ipc/shm.c @@ -198,7 +198,7 @@ static int __shm_open(struct vm_area_str return PTR_ERR(shp);
shp->shm_atim = get_seconds(); - shp->shm_lprid = task_tgid_vnr(current); + ipc_update_pid(&shp->shm_lprid, task_tgid(current)); shp->shm_nattch++; shm_unlock(shp); return 0; @@ -238,6 +238,8 @@ static void shm_destroy(struct ipc_names else if (shp->mlock_user) user_shm_unlock(file_inode(shm_file)->i_size, shp->mlock_user); fput(shm_file); + ipc_update_pid(&shp->shm_cprid, NULL); + ipc_update_pid(&shp->shm_lprid, NULL); ipc_rcu_putref(shp, shm_rcu_free); }
@@ -282,7 +284,7 @@ static void shm_close(struct vm_area_str if (WARN_ON_ONCE(IS_ERR(shp))) goto done; /* no-op */
- shp->shm_lprid = task_tgid_vnr(current); + ipc_update_pid(&shp->shm_lprid, task_tgid(current)); shp->shm_dtim = get_seconds(); shp->shm_nattch--; if (shm_may_destroy(ns, shp)) @@ -581,8 +583,8 @@ static int newseg(struct ipc_namespace * if (IS_ERR(file)) goto no_file;
- shp->shm_cprid = task_tgid_vnr(current); - shp->shm_lprid = 0; + shp->shm_cprid = get_pid(task_tgid(current)); + shp->shm_lprid = NULL; shp->shm_atim = shp->shm_dtim = 0; shp->shm_ctim = get_seconds(); shp->shm_segsz = size; @@ -614,6 +616,8 @@ no_id: user_shm_unlock(size, shp->mlock_user); fput(file); no_file: + ipc_update_pid(&shp->shm_cprid, NULL); + ipc_update_pid(&shp->shm_lprid, NULL); ipc_rcu_putref(shp, shm_rcu_free); return error; } @@ -952,8 +956,8 @@ static int shmctl_nolock(struct ipc_name tbuf.shm_atime = shp->shm_atim; tbuf.shm_dtime = shp->shm_dtim; tbuf.shm_ctime = shp->shm_ctim; - tbuf.shm_cpid = shp->shm_cprid; - tbuf.shm_lpid = shp->shm_lprid; + tbuf.shm_cpid = pid_vnr(shp->shm_cprid); + tbuf.shm_lpid = pid_vnr(shp->shm_lprid); tbuf.shm_nattch = shp->shm_nattch; rcu_read_unlock();
@@ -1363,6 +1367,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, sh #ifdef CONFIG_PROC_FS static int sysvipc_shm_proc_show(struct seq_file *s, void *it) { + struct pid_namespace *pid_ns = ipc_seq_pid_ns(s); struct user_namespace *user_ns = seq_user_ns(s); struct shmid_kernel *shp = it; unsigned long rss = 0, swp = 0; @@ -1383,8 +1388,8 @@ static int sysvipc_shm_proc_show(struct shp->shm_perm.id, shp->shm_perm.mode, shp->shm_segsz, - shp->shm_cprid, - shp->shm_lprid, + pid_nr_ns(shp->shm_cprid, pid_ns), + pid_nr_ns(shp->shm_lprid, pid_ns), shp->shm_nattch, from_kuid_munged(user_ns, shp->shm_perm.uid), from_kgid_munged(user_ns, shp->shm_perm.gid),