From f8b5918495be32807c4f878de959540eb63a9b9f Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Tue, 30 Jun 2015 14:58:45 -0700 Subject: ipc,sysv: make return -EIDRM when racing with RMID consistent The ipc_lock helper is used by all forms of sysv ipc to acquire the ipc object's spinlock. Upon error (bogus identifier), we always return -EINVAL, whether the problem be in the idr path or because we raced with a task performing RMID. For the later, however, all ipc related manpages, state the that for: EIDRM points to a removed identifier. And return: EINVAL Invalid value, or unaligned, etc. Which (EINVAL) should only return once the ipc resource is deleted. For all types of ipc this is done immediately upon a RMID command. However, shared memory behaves slightly different as it can merely mark a segment for deletion, and delay the actual freeing until there are no more active consumers. Per shmctl(IPC_RMID) manpage: "" Mark the segment to be destroyed. The segment will only actually be destroyed after the last process detaches it (i.e., when the shm_nattch member of the associated structure shmid_ds is zero). "" Unlike ipc_lock, paths that behave "correctly", at least per the manpage, involve controlling the ipc resource via *ctl(), doing the exact same validity check as ipc_lock after right acquiring the spinlock: if (!ipc_valid_object()) { err = -EIDRM; goto out_unlock; } Thus make ipc_lock consistent with the rest of ipc code and return -EIDRM in ipc_lock when !ipc_valid_object(). Signed-off-by: Davidlohr Bueso Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) (limited to 'ipc/util.c') diff --git a/ipc/util.c b/ipc/util.c index 3fdfabfdd9c3..b99038699fee 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -583,19 +583,22 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id) rcu_read_lock(); out = ipc_obtain_object_idr(ids, id); if (IS_ERR(out)) - goto err1; + goto err; spin_lock(&out->lock); - /* ipc_rmid() may have already freed the ID while ipc_lock - * was spinning: here verify that the structure is still valid + /* + * ipc_rmid() may have already freed the ID while ipc_lock() + * was spinning: here verify that the structure is still valid. + * Upon races with RMID, return -EIDRM, thus indicating that + * the ID points to a removed identifier. */ if (ipc_valid_object(out)) return out; spin_unlock(&out->lock); - out = ERR_PTR(-EINVAL); -err1: + out = ERR_PTR(-EIDRM); +err: rcu_read_unlock(); return out; } -- cgit v1.2.3-59-g8ed1b