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[Qemu-devel] [PATCH 15/17] userfaultfd: make userfaultfd_write non block
From: |
Andrea Arcangeli |
Subject: |
[Qemu-devel] [PATCH 15/17] userfaultfd: make userfaultfd_write non blocking |
Date: |
Fri, 3 Oct 2014 19:08:05 +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 62b827e..2667d0d 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -458,9 +458,7 @@ 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;
@@ -488,34 +486,12 @@ 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 16/17] powerpc: add remap_anon_pages and userfaultfd, (continued)
- [Qemu-devel] [PATCH 16/17] powerpc: add remap_anon_pages and userfaultfd, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 14/17] userfaultfd: add new syscall to provide memory externalization, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 01/17] mm: gup: add FOLL_TRIED, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 06/17] kvm: Faults which trigger IO release the mmap_sem, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 04/17] mm: gup: make get_user_pages_fast and __get_user_pages_fast latency conscious, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 11/17] mm: swp_entry_swapcount, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 15/17] userfaultfd: make userfaultfd_write non blocking,
Andrea Arcangeli <=
- [Qemu-devel] [PATCH 13/17] waitqueue: add nr wake parameter to __wake_up_locked_key, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 09/17] mm: PT lock: export double_pt_lock/unlock, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 07/17] mm: madvise MADV_USERFAULT: prepare vm_flags to allow more than 32bits, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages, Andrea Arcangeli, 2014/10/03