linux/tools
Nadav Amit 4410cbb5c9 selftests/vm/userfaultfd: wake after copy failure
When userfaultfd copy-ioctl fails since the PTE already exists, an -EEXIST
error is returned and the faulting thread is not woken.  The current
userfaultfd test does not wake the faulting thread in such case.  The
assumption is presumably that another thread set the PTE through copy/wp
ioctl and would wake the faulting thread or that alternatively the fault
handler would realize there is no need to "must_wait" and continue.  This
is not necessarily true.

There is an assumption that the "must_wait" tests in handle_userfault()
are sufficient to provide definitive answer whether the offending PTE is
populated or not.  However, userfaultfd_must_wait() test is lockless.
Consequently, concurrent calls to ptep_modify_prot_start(), for instance,
can clear the PTE and can cause userfaultfd_must_wait() to wrongly assume
it is not populated and a wait is needed.

There are therefore 3 options:
(1) Change the tests to wake on copy failure.
(2) Wake faulting thread unconditionally on zero/copy ioctls before
    returning -EEXIST.
(3) Change the userfaultfd_must_wait() to hold locks.

This patch took the first approach, but the others are valid solutions
with different tradeoffs.

Link: https://lkml.kernel.org/r/20210808020724.1022515-4-namit@vmware.com
Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-09-03 09:58:16 -07:00
..
accounting
arch tools headers UAPI: Sync files changed by the memfd_secret new syscall 2021-07-14 10:05:35 -03:00
bootconfig bootconfig: Share the checksum function with tools 2021-06-10 13:41:26 -04:00
bpf bpftool: Check malloc return value in mount_bpffs_for_pin 2021-07-15 20:01:36 +02:00
build tools build: Fix quiet cmd indentation 2021-05-17 12:10:03 +09:00
cgroup
debugging tools: Fix "the the" in a message in kernel-chktaint 2021-06-13 17:01:17 -06:00
edid
firewire
firmware
gpio
hv
iio
include tools headers: Remove broken definition of __LITTLE_ENDIAN 2021-07-14 14:39:36 -03:00
io_uring tools/io_uring/io_uring-cp: sync with liburing example 2021-08-13 08:58:11 -06:00
kvm/kvm_stat tools/kvm_stat: Fix documentation typo 2021-05-07 06:06:22 -04:00
laptop
leds
lib libbpf: Do not close un-owned FD 0 on errors 2021-08-07 01:39:15 +02:00
memory-model tools/memory-model: Fix smp_mb__after_spinlock() spelling 2021-05-10 16:27:20 -07:00
objtool A single ELF format fix for a section flags mismatch bug that breaks 2021-06-28 11:35:55 -07:00
pci
pcmcia
perf Revert "perf map: Fix dso->nsinfo refcounting" 2021-07-30 18:26:22 -03:00
power tools/power/x86/intel-speed-select: v1.10 release 2021-06-18 15:29:32 +02:00
rcu tools/rcu: Add drgn script to dump number of RCU callbacks 2021-05-10 15:39:19 -07:00
scripts tools build: Fix quiet cmd indentation 2021-05-17 12:10:03 +09:00
spi
testing selftests/vm/userfaultfd: wake after copy failure 2021-09-03 09:58:16 -07:00
thermal/tmon
time
tracing
usb treewide: remove editor modelines and cruft 2021-05-07 00:26:34 -07:00
virtio tools/virtio: fix build 2021-08-11 06:44:24 -04:00
vm tools/vm/page_owner_sort.c: check malloc() return 2021-06-29 10:53:47 -07:00
wmi
Makefile