Subject: + ipcmsg-document-barriers.patch added to -mm tree To: davidlohr@xxxxxx,aswin@xxxxxx,manfred@xxxxxxxxxxxxxxxx,riel@xxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Fri, 10 Jan 2014 15:19:36 -0800 The patch titled Subject: ipc,msg: document barriers has been added to the -mm tree. Its filename is ipcmsg-document-barriers.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/ipcmsg-document-barriers.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/ipcmsg-document-barriers.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Davidlohr Bueso <davidlohr@xxxxxx> Subject: ipc,msg: document barriers Both expunge_all() and pipeline_send() rely on both a nil msg value and a full barrier to guarantee the correct ordering when waking up a task. While its counter part at the receiving end is well documented for the lockless recv algorithm, we still need to document these specific smp_mb() calls. Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx> Cc: Aswin Chandramouleeswaran <aswin@xxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- ipc/msg.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff -puN ipc/msg.c~ipcmsg-document-barriers ipc/msg.c --- a/ipc/msg.c~ipcmsg-document-barriers +++ a/ipc/msg.c @@ -253,8 +253,14 @@ static void expunge_all(struct msg_queue struct msg_receiver *msr, *t; list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) { - msr->r_msg = NULL; + msr->r_msg = NULL; /* initialize expunge ordering */ wake_up_process(msr->r_tsk); + /* + * Ensure that the wakeup is visible before setting r_msg as + * the receiving end depends on it: either spinning on a nil, + * or dealing with -EAGAIN cases. See lockless reveice part 1 + * and 2 in do_msgrcv(). + */ smp_mb(); msr->r_msg = ERR_PTR(res); } @@ -638,15 +644,22 @@ static inline int pipelined_send(struct list_del(&msr->r_list); if (msr->r_maxsize < msg->m_ts) { + /* initialize pipelined send ordering */ msr->r_msg = NULL; wake_up_process(msr->r_tsk); - smp_mb(); + smp_mb(); /* see barrier comment below */ msr->r_msg = ERR_PTR(-E2BIG); } else { msr->r_msg = NULL; msq->q_lrpid = task_pid_vnr(msr->r_tsk); msq->q_rtime = get_seconds(); wake_up_process(msr->r_tsk); + /* + * Ensure that the wakeup is visible before + * setting r_msg, as the receiving end depends + * on it. See lockless reveice part 1 and 2 in + * do_msgrcv(). + */ smp_mb(); msr->r_msg = msg; @@ -654,6 +667,7 @@ static inline int pipelined_send(struct } } } + return 0; } @@ -716,6 +730,7 @@ long do_msgsnd(int msqid, long mtype, vo goto out_unlock0; } + /* enqueue the sender and prepare to block */ ss_add(msq, &s); if (!ipc_rcu_getref(msq)) { _ Patches currently in -mm which might be from davidlohr@xxxxxx are x86-mm-account-for-tlb-flushes-only-when-debugging.patch x86-mm-clean-up-inconsistencies-when-flushing-tlb-ranges.patch x86-mm-eliminate-redundant-page-table-walk-during-tlb-range-flushing.patch x86-mm-change-tlb_flushall_shift-for-ivybridge.patch mm-x86-revisit-tlb_flushall_shift-tuning-for-page-flushes-except-on-ivybridge.patch mm-mmapc-add-mlock_future_check-helper.patch mm-mlock-prepare-params-outside-critical-region.patch partitions-efi-complete-documentation-of-gpt-kernel-param-purpose.patch ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch ipc-semc-avoid-overflow-of-semop-undo-semadj-value-fix.patch ipc-semc-avoid-overflow-of-semop-undo-semadj-value-fix-2.patch ipc-introduce-ipc_valid_object-helper-to-sort-out-ipc_rmid-races.patch ipc-change-kern_ipc_permdeleted-type-to-bool.patch ipc-whitespace-cleanup.patch ipc-standardize-code-comments.patch ipc-remove-braces-for-single-statements.patch ipc-remove-useless-return-statement.patch ipc-simplify-sysvipc_proc_open-return.patch ipc-delete-seq_max-field-in-struct-ipc_ids.patch ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch ipcmsg-document-barriers.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html