On Wed, Nov 25, 2020 at 1:30 PM Linus Torvalds
wrote:
>
> I'm not sure I'm willing to write and test the real patch, but it
> doesn't look _too_ nasty from just looking at the code. The bookmark
> thing makes it important to only actually clear the bit at the end (as
> does the handoff case
On Tue, Nov 24, 2020 at 3:24 PM Linus Torvalds
wrote:
>
> I've applied your second patch (the smaller one that just takes a ref
> around the critical section). If somebody comes up with some great
> alternative, we can always revisit this.
Hmm.
I'm not sure about "great alternative", but it
On Tue 24-11-20 12:19:12, Matthew Wilcox wrote:
> On Mon, Nov 23, 2020 at 08:07:24PM -0800, Hugh Dickins wrote:
> > Twice now, when exercising ext4 looped on shmem huge pages, I have crashed
> > on the PF_ONLY_HEAD check inside PageWaiters(): ext4_finish_bio() calling
> > end_page_writeback()
On Tue, Nov 24, 2020 at 1:47 PM Hugh Dickins wrote:
>
> I think the unreferenced struct page asks for trouble.
I do agree.
I've applied your second patch (the smaller one that just takes a ref
around the critical section). If somebody comes up with some great
alternative, we can always revisit
On Tue, 24 Nov 2020, Linus Torvalds wrote:
> On Tue, Nov 24, 2020 at 12:16 PM Matthew Wilcox wrote:
> >
> > So my s/if/while/ suggestion is wrong and we need to do something to
> > prevent spurious wakeups. Unless we bury the spurious wakeup logic
> > inside wait_on_page_writeback() ...
>
> We
On Tue, Nov 24, 2020 at 12:16 PM Matthew Wilcox wrote:
>
> So my s/if/while/ suggestion is wrong and we need to do something to
> prevent spurious wakeups. Unless we bury the spurious wakeup logic
> inside wait_on_page_writeback() ...
We can certainly make the "if()" in that loop be a
On Tue, Nov 24, 2020 at 11:00:42AM -0800, Linus Torvalds wrote:
> On Tue, Nov 24, 2020 at 10:33 AM Matthew Wilcox wrote:
> >
> > We could fix this by turning that 'if' into a 'while' in
> > write_cache_pages().
>
> That might be the simplest patch indeed.
>
> At the same time, I do worry about
On Tue, Nov 24, 2020 at 10:33 AM Matthew Wilcox wrote:
>
> We could fix this by turning that 'if' into a 'while' in
> write_cache_pages().
That might be the simplest patch indeed.
At the same time, I do worry about other cases like this: while
spurious wakeup events are normal and happen in
On Tue, Nov 24, 2020 at 08:28:16AM -0800, Hugh Dickins wrote:
> On Tue, 24 Nov 2020, Matthew Wilcox wrote:
> > On Mon, Nov 23, 2020 at 08:07:24PM -0800, Hugh Dickins wrote:
> > >
> > > Then on crashing a second time, realized there's a stronger reason against
> > > that approach. If my testing
On Mon, 23 Nov 2020, Hugh Dickins wrote:
> On Mon, 23 Nov 2020, Linus Torvalds wrote:
> >
> > IOW, why couldn't we just make the __test_set_page_writeback()
> > increment the page count if the writeback flag wasn't already set, and
> > then make the end_page_writeback() do a put_page() after it
On Tue, 24 Nov 2020, Matthew Wilcox wrote:
> On Mon, Nov 23, 2020 at 08:07:24PM -0800, Hugh Dickins wrote:
> >
> > Then on crashing a second time, realized there's a stronger reason against
> > that approach. If my testing just occasionally crashes on that check,
> > when the page is reused for
On Mon, Nov 23, 2020 at 08:07:24PM -0800, Hugh Dickins wrote:
> Twice now, when exercising ext4 looped on shmem huge pages, I have crashed
> on the PF_ONLY_HEAD check inside PageWaiters(): ext4_finish_bio() calling
> end_page_writeback() calling wake_up_page() on tail of a shmem huge page,
> no
On Mon, 23 Nov 2020, Linus Torvalds wrote:
> On Mon, Nov 23, 2020 at 8:07 PM Hugh Dickins wrote:
> >
> > The problem is that PageWriteback is not accompanied by a page reference
> > (as the NOTE at the end of test_clear_page_writeback() acknowledges): as
> > soon as TestClearPageWriteback has
On Mon, Nov 23, 2020 at 8:07 PM Hugh Dickins wrote:
>
> Then on crashing a second time, realized there's a stronger reason against
> that approach. If my testing just occasionally crashes on that check,
> when the page is reused for part of a compound page, wouldn't it be much
> more common for
On Mon, Nov 23, 2020 at 8:07 PM Hugh Dickins wrote:
>
> The problem is that PageWriteback is not accompanied by a page reference
> (as the NOTE at the end of test_clear_page_writeback() acknowledges): as
> soon as TestClearPageWriteback has been done, that page could be removed
> from page cache,
On Mon, 30 Aug 2020, Linus Torvalds wrote:
> On Mon, Aug 31, 2020 at 3:03 AM Jan Kara wrote:
> >
> > On Fri 28-08-20 12:07:55, Jan Kara wrote:
> > >
> > > Doh, so this is:
> > >
> > > wait_on_page_writeback(page);
> > > >>> BUG_ON(PageWriteback(page));
On Mon, Aug 31, 2020 at 3:03 AM Jan Kara wrote:
>
> On Fri 28-08-20 12:07:55, Jan Kara wrote:
> >
> > Doh, so this is:
> >
> > wait_on_page_writeback(page);
> > >>> BUG_ON(PageWriteback(page));
> >
> > in mpage_prepare_extent_to_map(). So we have
On Fri 28-08-20 12:07:55, Jan Kara wrote:
> On Wed 26-08-20 19:48:16, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel..
> > git tree: upstream
> > console output:
On Wed 26-08-20 19:48:16, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15f83cb690
> kernel config:
Hello,
syzbot found the following issue on:
HEAD commit:c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f83cb690
kernel config: https://syzkaller.appspot.com/x/.config?x=bb68b9e8a8cc842f
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