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cbcfa130a9
When IOCB_CMD_POLL is used on a userfaultfd, aio_poll() disables IRQs
and takes kioctx::ctx_lock, then userfaultfd_ctx::fd_wqh.lock.
This may have to wait for userfaultfd_ctx::fd_wqh.lock to be released by
userfaultfd_ctx_read(), which in turn can be waiting for
userfaultfd_ctx::fault_pending_wqh.lock or
userfaultfd_ctx::event_wqh.lock.
But elsewhere the fault_pending_wqh and event_wqh locks are taken with
IRQs enabled. Since the IRQ handler may take kioctx::ctx_lock, lockdep
reports that a deadlock is possible.
Fix it by always disabling IRQs when taking the fault_pending_wqh and
event_wqh locks.
Commit ae62c16e105a ("userfaultfd: disable irqs when taking the
waitqueue lock") didn't fix this because it only accounted for the
fd_wqh lock, not the other locks nested inside it.
Link: http://lkml.kernel.org/r/20190627075004.21259-1-ebiggers@kernel.org
Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reported-by: syzbot+fab6de82892b6b9c6191@syzkaller.appspotmail.com
Reported-by: syzbot+53c0b767f7ca0dc0c451@syzkaller.appspotmail.com
Reported-by: syzbot+a3accb352f9c22041cfa@syzkaller.appspotmail.com
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org> [4.19+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.