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[Qemu-devel] [PATCH 09/10] userfaultfd: make userfaultfd_write non block
From: |
Andrea Arcangeli |
Subject: |
[Qemu-devel] [PATCH 09/10] userfaultfd: make userfaultfd_write non blocking |
Date: |
Wed, 2 Jul 2014 18:50:15 +0200 |
It is generally inefficient to ask the wakeup of userfault ranges
where there's not a single userfault address read through
userfaultfd_read earlier and in turn waiting a wakeup. However it may
come handy to wakeup the same userfault range twice in case of
multiple thread faulting on the same address. But we should still
return an error so if the application thinks this occurrence can never
happen it will know it hit a bug. So just return -ENOENT instead of
blocking.
Signed-off-by: Andrea Arcangeli <address@hidden>
---
fs/userfaultfd.c | 34 +++++-----------------------------
1 file changed, 5 insertions(+), 29 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 4902fa3..deed8cb 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -378,9 +378,7 @@ static ssize_t userfaultfd_write(struct file *file, const
char __user *buf,
size_t count, loff_t *ppos)
{
struct userfaultfd_ctx *ctx = file->private_data;
- ssize_t res;
__u64 range[2];
- DECLARE_WAITQUEUE(wait, current);
if (ctx->state == USERFAULTFD_STATE_ASK_PROTOCOL) {
__u64 protocol;
@@ -408,34 +406,12 @@ static ssize_t userfaultfd_write(struct file *file, const
char __user *buf,
if (range[0] >= range[1])
return -ERANGE;
- spin_lock(&ctx->fd_wqh.lock);
- __add_wait_queue(&ctx->fd_wqh, &wait);
- for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
- /* always take the fd_wqh lock before the fault_wqh lock */
- if (find_userfault(ctx, NULL, POLLOUT)) {
- if (!wake_userfault(ctx, range)) {
- res = sizeof(range);
- break;
- }
- }
- if (signal_pending(current)) {
- res = -ERESTARTSYS;
- break;
- }
- if (file->f_flags & O_NONBLOCK) {
- res = -EAGAIN;
- break;
- }
- spin_unlock(&ctx->fd_wqh.lock);
- schedule();
- spin_lock(&ctx->fd_wqh.lock);
- }
- __remove_wait_queue(&ctx->fd_wqh, &wait);
- __set_current_state(TASK_RUNNING);
- spin_unlock(&ctx->fd_wqh.lock);
+ /* always take the fd_wqh lock before the fault_wqh lock */
+ if (find_userfault(ctx, NULL, POLLOUT))
+ if (!wake_userfault(ctx, range))
+ return sizeof(range);
- return res;
+ return -ENOENT;
}
#ifdef CONFIG_PROC_FS
- [Qemu-devel] [PATCH 00/10] RFC: userfault, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 01/10] mm: madvise MADV_USERFAULT: prepare vm_flags to allow more than 32bits, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 02/10] mm: madvise MADV_USERFAULT, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 07/10] waitqueue: add nr wake parameter to __wake_up_locked_key, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 04/10] mm: rmap preparation for remap_anon_pages, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 05/10] mm: swp_entry_swapcount, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 09/10] userfaultfd: make userfaultfd_write non blocking,
Andrea Arcangeli <=
- [Qemu-devel] [PATCH 10/10] userfaultfd: use VM_FAULT_RETRY in handle_userfault(), Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 06/10] mm: sys_remap_anon_pages, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 08/10] userfaultfd: add new syscall to provide memory externalization, Andrea Arcangeli, 2014/07/02
- [Qemu-devel] [PATCH 03/10] mm: PT lock: export double_pt_lock/unlock, Andrea Arcangeli, 2014/07/02
- Re: [Qemu-devel] [PATCH 00/10] RFC: userfault, Andy Lutomirski, 2014/07/02
- Re: [Qemu-devel] [PATCH 00/10] RFC: userfault, Christopher Covington, 2014/07/03