I manage eight Fedora 25 desktop machines of different makes which all are updated in tandem. This morning I ran `sudo sh -c 'dnf update -y && reboot'` on all of them, and two of them did not come back up. Based on the logs it appears the problem is with libgtk-3.so.0.2200.11. From dmesg on machine 1:

gnome-session-f[5292]: segfault at 0 ip 00007f46a0aa94e9 sp 00007ffc4b398840 error 4 in libgtk-3.so.0.2200.11[7f46a07ca000+6f9000]
gnome-session-f[5713]: segfault at 0 ip 00007fdc1d4a54e9 sp 00007ffce01ed260 error 4 in libgtk-3.so.0.2200.11[7fdc1d1c6000+6f9000]

On machine 2:

gnome-session-f[3160]: segfault at 0 ip 00007f2ea97674e9 sp 00007ffc23562d80 error 4 in libgtk-3.so.0.2200.11[7f2ea9488000+6f9000]

From /var/log/dnf.log, the list of updated packages:

gnutls.x86_64 3.5.11-1.fc25
ibus-typing-booster.noarch 1.5.31-1.fc25
js-jquery.noarch 2.2.4-3.fc25
libipa_hbac.x86_64 1.15.2-2.fc25
libsemanage.x86_64 2.5-9.fc25
libsemanage-python.x86_64 2.5-9.fc25
libsemanage-python3.x86_64 2.5-9.fc25
libsss_autofs.x86_64 1.15.2-2.fc25
libsss_idmap.x86_64 1.15.2-2.fc25
libsss_nss_idmap.x86_64 1.15.2-2.fc25
libsss_sudo.x86_64 1.15.2-2.fc25
nfs-utils.x86_64 1:2.1.1-4.rc2.fc25
nss-softokn.x86_64 3.29.5-1.0.fc25
nss-softokn-freebl.x86_64 3.29.5-1.0.fc25
nss-util.x86_64 3.29.5-1.0.fc25
python3-sssdconfig.noarch 1.15.2-2.fc25
sssd.x86_64 1.15.2-2.fc25
sssd-ad.x86_64 1.15.2-2.fc25
sssd-client.x86_64 1.15.2-2.fc25
sssd-common.x86_64 1.15.2-2.fc25
sssd-common-pac.x86_64 1.15.2-2.fc25
sssd-ipa.x86_64 1.15.2-2.fc25
sssd-krb5.x86_64 1.15.2-2.fc25
sssd-krb5-common.x86_64 1.15.2-2.fc25
sssd-ldap.x86_64 1.15.2-2.fc25
sssd-nfs-idmap.x86_64 1.15.2-2.fc25
sssd-proxy.x86_64 1.15.2-2.fc25
xorg-x11-drv-nouveau.x86_64 1:1.0.14-1.fc25

Workaround: Downgrade the Nouveau driver:

sudo dnf install xorg-x11-drv-nouveau-1\:1.0.13-1.fc25.x86_64

Worked for both machines.

$ uname -srvmo
Linux 4.10.10-200.fc25.x86_64 #1 SMP Thu Apr 13 01:11:51 UTC 2017 x86_64 GNU/Linux

[As reported at https://bugzilla.gnome.org/show_bug.cgi?id=781576]