diff mbox series

[2/2] MIPS/c-r4k: do no use mmap_sem for gup_fast()

Message ID 20190207053740.26915-3-dave@stgolabs.net (mailing list archive)
State New, archived
Headers show
Series more get_user_pages mmap_sem cleanups | expand

Commit Message

Davidlohr Bueso Feb. 7, 2019, 5:37 a.m. UTC 
It is well known that because the mm can internally
call the regular gup_unlocked if the lockless approach
fails and take the sem there, the caller must not hold
the mmap_sem already.

Fixes: e523f289fe4d (MIPS: c-r4k: Fix sigtramp SMP call to use kmap)
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 arch/mips/mm/c-r4k.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Comments

Paul Burton Feb. 7, 2019, 7 p.m. UTC | #1 
Hi Davidlohr,

On Wed, Feb 06, 2019 at 09:37:40PM -0800, Davidlohr Bueso wrote:
> It is well known that because the mm can internally
> call the regular gup_unlocked if the lockless approach
> fails and take the sem there, the caller must not hold
> the mmap_sem already.
> 
> Fixes: e523f289fe4d (MIPS: c-r4k: Fix sigtramp SMP call to use kmap)
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: Paul Burton <paul.burton@mips.com>
> Cc: James Hogan <jhogan@kernel.org>
> Cc: linux-mips@vger.kernel.org
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

Thanks - this looks good, but:

 1) The problem it fixes was introduced in v4.8.

 2) Commit adcc81f148d7 ("MIPS: math-emu: Write-protect delay slot
    emulation pages") actually left flush_cache_sigtramp unused, and has
    been backported to stable kernels also as far as v4.8.

Therefore this will just fix code that never gets called, and I'll go
delete the whole thing instead.

Thanks,
    Paul
Davidlohr Bueso Feb. 7, 2019, 7:25 p.m. UTC | #2 
On Thu, 07 Feb 2019, Paul Burton wrote:

>Hi Davidlohr,
>
>On Wed, Feb 06, 2019 at 09:37:40PM -0800, Davidlohr Bueso wrote:
>> It is well known that because the mm can internally
>> call the regular gup_unlocked if the lockless approach
>> fails and take the sem there, the caller must not hold
>> the mmap_sem already.
>>
>> Fixes: e523f289fe4d (MIPS: c-r4k: Fix sigtramp SMP call to use kmap)
>> Cc: Ralf Baechle <ralf@linux-mips.org>
>> Cc: Paul Burton <paul.burton@mips.com>
>> Cc: James Hogan <jhogan@kernel.org>
>> Cc: linux-mips@vger.kernel.org
>> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
>
>Thanks - this looks good, but:
>
> 1) The problem it fixes was introduced in v4.8.
>
> 2) Commit adcc81f148d7 ("MIPS: math-emu: Write-protect delay slot
>    emulation pages") actually left flush_cache_sigtramp unused, and has
>    been backported to stable kernels also as far as v4.8.
>
>Therefore this will just fix code that never gets called, and I'll go
>delete the whole thing instead.

Even better.

Thanks,
Davidlohr
diff mbox series

Patch

diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index cc4e17caeb26..38fe86928837 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -1034,11 +1034,9 @@  static void r4k_flush_cache_sigtramp(unsigned long addr)
 	struct flush_cache_sigtramp_args args;
 	int npages;
 
-	down_read(&current->mm->mmap_sem);
-
 	npages = get_user_pages_fast(addr, 1, 0, &args.page);
 	if (npages < 1)
-		goto out;
+		return;
 
 	args.mm = current->mm;
 	args.addr = addr;
@@ -1046,8 +1044,6 @@  static void r4k_flush_cache_sigtramp(unsigned long addr)
 	r4k_on_each_cpu(R4K_HIT, local_r4k_flush_cache_sigtramp, &args);
 
 	put_page(args.page);
-out:
-	up_read(&current->mm->mmap_sem);
 }
 
 static void r4k_flush_icache_all(void)