The patch titled
Subject: userfaultfd: disable irqs when taking the waitqueue lock
has been added to the -mm tree. Its filename is
userfaultfd-disable-irqs-when-taking-the-waitqueue-lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-disable-irqs-when-taking-the-waitqueue-lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-disable-irqs-when-taking-the-waitqueue-lock.patch
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------------------------------------------------------
From: Christoph Hellwig <hch@xxxxxx>
Subject: userfaultfd: disable irqs when taking the waitqueue lock
userfaultfd contains howe-grown locking of the waitqueue lock, and does
not disable interrupts. This relies on the fact that no one else takes it
from interrupt context and violates an invariat of the normal waitqueue
locking scheme. With aio poll it is easy to trigger other locks that
disable interrupts (or are called from interrupt context).
Link: http://lkml.kernel.org/r/20181018154101.18750-1-hch@xxxxxx
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/fs/userfaultfd.c~userfaultfd-disable-irqs-when-taking-the-waitqueue-lock
+++ a/fs/userfaultfd.c
@@ -1026,7 +1026,7 @@ static ssize_t userfaultfd_ctx_read(stru
struct userfaultfd_ctx *fork_nctx = NULL;
/* always take the fd_wqh lock before the fault_pending_wqh lock */
- spin_lock(&ctx->fd_wqh.lock);
+ spin_lock_irq(&ctx->fd_wqh.lock);
__add_wait_queue(&ctx->fd_wqh, &wait);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -1112,13 +1112,13 @@ static ssize_t userfaultfd_ctx_read(stru
ret = -EAGAIN;
break;
}
- spin_unlock(&ctx->fd_wqh.lock);
+ spin_unlock_irq(&ctx->fd_wqh.lock);
schedule();
- spin_lock(&ctx->fd_wqh.lock);
+ spin_lock_irq(&ctx->fd_wqh.lock);
}
__remove_wait_queue(&ctx->fd_wqh, &wait);
__set_current_state(TASK_RUNNING);
- spin_unlock(&ctx->fd_wqh.lock);
+ spin_unlock_irq(&ctx->fd_wqh.lock);
if (!ret && msg->event == UFFD_EVENT_FORK) {
ret = resolve_userfault_fork(ctx, fork_nctx, msg);
_
Patches currently in -mm which might be from hch@xxxxxx are
userfaultfd-disable-irqs-when-taking-the-waitqueue-lock.patch
