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    Subject[PATCH v5 21/25] userfaultfd: wp: don't wake up when doing write protect
    Date
    It does not make sense to try to wake up any waiting thread when we're
    write-protecting a memory region. Only wake up when resolving a write
    protected page fault.

    Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
    Signed-off-by: Peter Xu <peterx@redhat.com>
    ---
    fs/userfaultfd.c | 13 ++++++++-----
    1 file changed, 8 insertions(+), 5 deletions(-)

    diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
    index 3cf19aeaa0e0..498971fa9163 100644
    --- a/fs/userfaultfd.c
    +++ b/fs/userfaultfd.c
    @@ -1782,6 +1782,7 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
    struct uffdio_writeprotect uffdio_wp;
    struct uffdio_writeprotect __user *user_uffdio_wp;
    struct userfaultfd_wake_range range;
    + bool mode_wp, mode_dontwake;

    if (READ_ONCE(ctx->mmap_changing))
    return -EAGAIN;
    @@ -1800,18 +1801,20 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
    if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
    UFFDIO_WRITEPROTECT_MODE_WP))
    return -EINVAL;
    - if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) &&
    - (uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE))
    +
    + mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
    + mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
    +
    + if (mode_wp && mode_dontwake)
    return -EINVAL;

    ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
    - uffdio_wp.range.len, uffdio_wp.mode &
    - UFFDIO_WRITEPROTECT_MODE_WP,
    + uffdio_wp.range.len, mode_wp,
    &ctx->mmap_changing);
    if (ret)
    return ret;

    - if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) {
    + if (!mode_wp && !mode_dontwake) {
    range.start = uffdio_wp.range.start;
    range.len = uffdio_wp.range.len;
    wake_userfault(ctx, &range);
    --
    2.21.0
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