lkml.org 
[lkml]   [2023]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Converting dev->mutex into dev->spinlock ?
    On Sat, Feb 04, 2023 at 11:21:27PM +0900, Tetsuo Handa wrote:
    > On 2023/02/04 22:47, Greg Kroah-Hartman wrote:
    > > On Sat, Feb 04, 2023 at 10:32:11PM +0900, Tetsuo Handa wrote:
    > >> Hello.
    > >>
    > >> There is a long-standing deadlock problem in driver core code caused by
    > >> "struct device"->mutex being marked as "do not apply lockdep checks".
    > >
    > > The marking of a lock does not cause a deadlock problem, so what do you
    > > mean exactly by this? Where is the actual deadlock?
    >
    > A few of examples:
    >
    > https://syzkaller.appspot.com/bug?extid=2d6ac90723742279e101
    > https://syzkaller.appspot.com/bug?extid=2e39bc6569d281acbcfb
    > https://syzkaller.appspot.com/bug?extid=9ef743bba3a17c756174

    Random links to syzkaller reports that are huge and not descriptive does
    not actually persuade me as I don't have the inclination to dig through
    them, sorry.

    Specific examples, with code, please.

    > >> We can make this deadlock visible by applying [1], and we can confirm that
    > >> there is a deadlock problem that I think needs to be addressed in core code [2].
    > >
    > > Any reason why you didn't cc: us on these patches?
    >
    > We can't apply this "drivers/core: Remove lockdep_set_novalidate_class() usage" patch

    What patch is that? I do not see that in my inbox anywhere. I don't
    even see it in my lkml archive, so I do not know what you are talking
    about.

    > until we fix all lockdep warnings that happen during the boot stage;

    What lockdep warnings?

    > otherwise syzbot testing can't work which is more painful than
    > applying this patch now.

    Again, I'm totally confused. What is the real bug/problem/issue here?

    Where is the deadlock?

    > Therefore, I locally tested this patch (in order not to be applied now).

    What patch? I'm totally confused.

    > And I got a lockdep warning on the perf_event code.

    What warning?

    > I got next lockdep warning on the driver core code when I tried a fix
    > for the perf_event code suggested by Peter Zijlstra.

    Again, what warning?

    > Since Peter confirmed that this is a problem that led to commit
    > 1704f47b50b5 ("lockdep: Add novalidate class for dev->mutex
    > conversion"), this time I'm reporting this problem to you (so that you
    > can propose a fix for the driver core code).

    Again, I have no idea what the real problem is!

    Please show me in the driver core code, where the deadlock is that needs
    to be resolved. Without that, I can't answer anything...

    totally and throughly confused,

    greg k-h

    \
     
     \ /
      Last update: 2023-03-27 00:09    [W:4.522 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site