The patch titled
Subject: userfaultfd: use fault_wqh lock
has been added to the -mm tree. Its filename is
userfaultfd-use-fault_wqh-lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-use-fault_wqh-lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-use-fault_wqh-lock.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: userfaultfd: use fault_wqh lock
The userfaultfd code currently uses the unlocked waitqueue helpers for
managing fault_wqh, but instead of holding the waitqueue lock for this
waitqueue around these calls, it the waitqueue lock of
fault_pending_wq, which is a different waitqueue instance. Given that
the waitqueue is not exposed to the rest of the kernel this actually
works ok at the moment, but prevents the userfaultfd locking rules from
being enforced using lockdep.
Switch to the internally locked waitqueue helpers instead. This means
that the lock inside fault_wqh now nests inside the fault_pending_wqh
lock, but that's not a problem since it was entirely unused before.
[hch@xxxxxx: slight changelog updates]
[rppt@xxxxxxxxxxxxxxxxxx: spotted changelog spellos]
Link: http://lkml.kernel.org/r/20171214152344.6880-3-hch@xxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN fs/userfaultfd.c~userfaultfd-use-fault_wqh-lock fs/userfaultfd.c
--- a/fs/userfaultfd.c~userfaultfd-use-fault_wqh-lock
+++ a/fs/userfaultfd.c
@@ -908,7 +908,7 @@ wakeup:
*/
spin_lock(&ctx->fault_pending_wqh.lock);
__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
- __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
+ __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
spin_unlock(&ctx->fault_pending_wqh.lock);
/* Flush pending events that may still wait on event_wqh */
@@ -1064,7 +1064,7 @@ static ssize_t userfaultfd_ctx_read(stru
* anyway.
*/
list_del(&uwq->wq.entry);
- __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
+ add_wait_queue(&ctx->fault_wqh, &uwq->wq);
write_seqcount_end(&ctx->refile_seq);
@@ -1213,7 +1213,7 @@ static void __wake_userfault(struct user
__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
range);
if (waitqueue_active(&ctx->fault_wqh))
- __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
+ __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
spin_unlock(&ctx->fault_pending_wqh.lock);
}
_
Patches currently in -mm which might be from mawilcox@xxxxxxxxxxxxx are
userfaultfd-use-fault_wqh-lock.patch
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