On Tue, Jul 25, 2017 at 10:28:16AM +0200, Michael Wang wrote: > Hi, greg k-h > > During our testing with 4.4.73 we got soft lockup like: > > NMI watchdog: BUG: soft lockup - CPU#2 stuck for 23s! [systemd-udevd:856] > ... > Call Trace: > [<ffffffff8109d139>] vprintk_emit+0x319/0x4a0 > [<ffffffff8112182d>] printk_emit+0x33/0x3b > [<ffffffff812f9e9c>] ? simple_strtoull+0x2c/0x50 > [<ffffffff8109d39a>] devkmsg_write+0xaa/0x100 > [<ffffffff8109d2f0>] ? vprintk+0x30/0x30 > [<ffffffff811915f2>] do_readv_writev+0x1c2/0x270 > [<ffffffff8117899d>] ? kmem_cache_free+0x7d/0x1a0 > [<ffffffff81191729>] vfs_writev+0x39/0x50 > [<ffffffff8119240a>] SyS_writev+0x4a/0xd0 > [<ffffffff8158bc97>] entry_SYSCALL_64_fastpath+0x12/0x6a > > Currently in 4.4 the console_unlock() called by vprintk_emit() is with > preemption disabled, so the cond_resched is not working, and soft lockup > appear if it take too much time on writing data into every console. > > We found the upstream patch: > commit 6b97a20d3a79 printk: set may_schedule for some of console_trylock() callers > > which should have addressed this issue, but not included in the latest 4.4.78 stable > yet, is there any plan on backport it in future? That commit was in the 4.6 kernel release, so odds are, it's not on a list of patches to backport any time soon :) But, you can ask for it to be included, if you cc: the stable@vger list, like I did here, and add the authors of the patch to the cc: asking if they have any objection for it being backported (also added here...) Sergey, any objection for me backporting this? thanks, greg k-h