Messages in this thread | | | Subject | Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL. | From | Tetsuo Handa <> | Date | Mon, 26 Aug 2019 22:44:29 +0900 |
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On 2019/08/26 22:29, Greg Kroah-Hartman wrote: > On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote: >> syzbot found that a thread can stall for minutes inside read_mem() or >> write_mem() after that thread was killed by SIGKILL [1]. Reading from >> iomem areas of /dev/mem can be slow, depending on the hardware. >> While reading 2GB at one read() is legal, delaying termination of killed >> thread for minutes is bad. Thus, allow reading/writing /dev/mem and >> /dev/kmem to be preemptible and killable. >> >> [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632 >> [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536 >> [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440 >> [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344 >> [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248 >> >> Theoretically, reading/writing /dev/mem and /dev/kmem can become >> "interruptible". But this patch chose "killable". Future patch will make >> them "interruptible" so that we can revert to "killable" if some program >> regressed. >> >> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e >> >> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> >> Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com> >> --- >> drivers/char/mem.c | 21 +++++++++++++++++++++ >> 1 file changed, 21 insertions(+) > > What changed from previous versions? > > That goes below the --- line at the very least.
(1) Moved fatal_signal_pending() test to end of iteration. (2) Added need_resched() test before cond_resched(). (3) Removed -EINTR assignment because end of iteration means that at least one byte was processed (sz > 0).
> > thanks, > > greg k-h >
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