On Thu, 17 Jan 2008 17:39:54 -0600
Matt Mackall <[EMAIL PROTECTED]> wrote:
>
> On Thu, 2008-01-17 at 14:51 -0800, Andrew Morton wrote:
> > > proc_loop: /proc/3731/task/3731/pagemap
> > > kernel: BUG: sleeping function called from invalid context at
> > > fs/proc/task_mmu.c:554
> > > kernel: in_atomic():1, irqs_disabled():0
> > > kernel: Call Trace:
> > > kernel: [cf1cddf0] [c000840c] show_stack+0x3c/0x194 (unreliable)
> > > kernel: [cf1cde20] [c002b2ec] __might_sleep+0xf4/0x108
> > > kernel: [cf1cde30] [c00d2d54] add_to_pagemap+0x40/0x11c
> > > kernel: [cf1cde50] [c00d2f44] pagemap_pte_range+0xa8/0x10c
> > > kernel: [cf1cde70] [c0081b30] walk_page_range+0x148/0x23c
> > > kernel: [cf1cdeb0] [c00d3104] pagemap_read+0x15c/0x244
> > > kernel: [cf1cdef0] [c0092144] vfs_read+0xc4/0x16c
> > > kernel: [cf1cdf10] [c009261c] sys_read+0x4c/0x90
> > > kernel: [cf1cdf40] [c001328c] ret_from_syscall+0x0/0x40
> >
> > It's not really an oops - it's a warning. add_to_pagemap() is doing a
> > put_user() inside pagemap_pte_range->pte_offset_map->kmap_atomic.
> >
> > A known bug, I'm afraid.
> >
> > How to fix?
> >
> > - double-buffer the data to be copied to userspace or
> >
> > - take a local copy of the pte page then work on that instead or
> >
> > - play copy_to_user_inatomic() tricks.
>
> Hmm, this fell off my radar. How about something like this as a minimal
> fix (untested as -mm is a complete doorstop for me at the moment)?
>
> diff -r 5595adaea70f fs/proc/task_mmu.c
> --- a/fs/proc/task_mmu.c Thu Jan 17 13:26:54 2008 -0600
> +++ b/fs/proc/task_mmu.c Thu Jan 17 17:29:21 2008 -0600
> @@ -582,20 +583,26 @@
> {
> struct pagemapread *pm = private;
> pte_t *pte;
> - int err = 0;
> + int offset = 0, err = 0;
>
> pte = pte_offset_map(pmd, addr);
> - for (; addr != end; pte++, addr += PAGE_SIZE) {
> + for (; addr != end; offset++, addr += PAGE_SIZE) {
> u64 pfn = PM_NOT_PRESENT;
> - if (is_swap_pte(*pte))
> - pfn = swap_pte_to_pagemap_entry(*pte);
> - else if (pte_present(*pte))
> - pfn = pte_pfn(*pte);
> + if (is_swap_pte(pte[offset]))
> + pfn = swap_pte_to_pagemap_entry(pte[offset]);
> + else if (pte_present(pte[offset]))
> + pfn = pte_pfn(pte[offset]);
> +#ifdef CONFIG_HIGHPTE
> + pte_unmap(pte);
> err = add_to_pagemap(addr, pfn, pm);
> + pte = pte_offset_map(pmd, addr);
> +#else
> + err = add_to_pagemap(addr, pfn, pm);
> +#endif
> if (err)
> return err;
> }
> - pte_unmap(pte - 1);
> + pte_unmap(pte);
>
> cond_resched();
>
Good point, it really can be taht simple.
Do we need the ifdef? pte_offset_map/pte_unmap should be super-cheap on
!CONFIG_HIGHPTE builds.
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