| Message ID | 20240611182732.360317-2-martin.oliveira@eideticom.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Enable P2PDMA in Userspace RDMA | expand |
On Tue, Jun 11, 2024 at 12:27:29PM -0600, Martin Oliveira wrote: > The .page_mkwrite operator of kernfs just calls file_update_time(). > This is the same behaviour that the fault code does if .page_mkwrite is > not set. > > Furthermore, having the page_mkwrite() operator causes > writable_file_mapping_allowed() to fail due to > vma_needs_dirty_tracking() on the gup flow, which is a pre-requisite for > enabling P2PDMA over RDMA. > > There are no users of .page_mkwrite and no known valid use cases, so > just remove the .page_mkwrite from kernfs_ops and return -EINVAL if an > mmap() implementation sets .page_mkwrite. > > Co-developed-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com> > --- > fs/kernfs/file.c | 26 +++----------------------- > 1 file changed, 3 insertions(+), 23 deletions(-) Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
On Tue, Jun 11, 2024 at 12:27:29PM -0600, Martin Oliveira wrote: > The .page_mkwrite operator of kernfs just calls file_update_time(). > This is the same behaviour that the fault code does if .page_mkwrite is > not set. > > Furthermore, having the page_mkwrite() operator causes > writable_file_mapping_allowed() to fail due to > vma_needs_dirty_tracking() on the gup flow, which is a pre-requisite for > enabling P2PDMA over RDMA. > > There are no users of .page_mkwrite and no known valid use cases, so > just remove the .page_mkwrite from kernfs_ops and return -EINVAL if an > mmap() implementation sets .page_mkwrite. > > Co-developed-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com> Acked-by: Tejun Heo <tj@kernel.org> Thanks.
Hi Martin,
kernel test robot noticed the following build warnings:
url: https://github.com/intel-lab-lkp/linux/commits/Martin-Oliveira/kernfs-remove-page_mkwrite-from-vm_operations_struct/20240612-023130
base: 83a7eefedc9b56fe7bfeff13b6c7356688ffa670
patch link: https://lore.kernel.org/r/20240611182732.360317-2-martin.oliveira%40eideticom.com
patch subject: [PATCH v2 1/4] kernfs: remove page_mkwrite() from vm_operations_struct
config: i386-randconfig-141-20240612 (https://download.01.org/0day-ci/archive/20240613/202406130357.6NmgCbMP-lkp@intel.com/config)
compiler: gcc-12 (Ubuntu 12.3.0-9ubuntu2) 12.3.0
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202406130357.6NmgCbMP-lkp@intel.com/
smatch warnings:
fs/kernfs/file.c:462 kernfs_fop_mmap() error: we previously assumed 'vma->vm_ops' could be null (see line 459)
vim +462 fs/kernfs/file.c
c637b8acbe079e Tejun Heo 2013-12-11 416 static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
414985ae23c031 Tejun Heo 2013-11-28 417 {
c525aaddc366df Tejun Heo 2013-12-11 418 struct kernfs_open_file *of = kernfs_of(file);
414985ae23c031 Tejun Heo 2013-11-28 419 const struct kernfs_ops *ops;
414985ae23c031 Tejun Heo 2013-11-28 420 int rc;
414985ae23c031 Tejun Heo 2013-11-28 421
9b2db6e1894577 Tejun Heo 2013-12-10 422 /*
9b2db6e1894577 Tejun Heo 2013-12-10 423 * mmap path and of->mutex are prone to triggering spurious lockdep
9b2db6e1894577 Tejun Heo 2013-12-10 424 * warnings and we don't want to add spurious locking dependency
9b2db6e1894577 Tejun Heo 2013-12-10 425 * between the two. Check whether mmap is actually implemented
9b2db6e1894577 Tejun Heo 2013-12-10 426 * without grabbing @of->mutex by testing HAS_MMAP flag. See the
c810729fe6471a Ahelenia Ziemiańska 2023-12-21 427 * comment in kernfs_fop_open() for more details.
9b2db6e1894577 Tejun Heo 2013-12-10 428 */
df23fc39bce03b Tejun Heo 2013-12-11 429 if (!(of->kn->flags & KERNFS_HAS_MMAP))
9b2db6e1894577 Tejun Heo 2013-12-10 430 return -ENODEV;
9b2db6e1894577 Tejun Heo 2013-12-10 431
414985ae23c031 Tejun Heo 2013-11-28 432 mutex_lock(&of->mutex);
414985ae23c031 Tejun Heo 2013-11-28 433
414985ae23c031 Tejun Heo 2013-11-28 434 rc = -ENODEV;
c637b8acbe079e Tejun Heo 2013-12-11 435 if (!kernfs_get_active(of->kn))
414985ae23c031 Tejun Heo 2013-11-28 436 goto out_unlock;
414985ae23c031 Tejun Heo 2013-11-28 437
324a56e16e44ba Tejun Heo 2013-12-11 438 ops = kernfs_ops(of->kn);
414985ae23c031 Tejun Heo 2013-11-28 439 rc = ops->mmap(of, vma);
b44b2140265ddf Tejun Heo 2014-04-20 440 if (rc)
b44b2140265ddf Tejun Heo 2014-04-20 441 goto out_put;
414985ae23c031 Tejun Heo 2013-11-28 442
414985ae23c031 Tejun Heo 2013-11-28 443 /*
414985ae23c031 Tejun Heo 2013-11-28 444 * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
414985ae23c031 Tejun Heo 2013-11-28 445 * to satisfy versions of X which crash if the mmap fails: that
414985ae23c031 Tejun Heo 2013-11-28 446 * substitutes a new vm_file, and we don't then want bin_vm_ops.
414985ae23c031 Tejun Heo 2013-11-28 447 */
414985ae23c031 Tejun Heo 2013-11-28 448 if (vma->vm_file != file)
414985ae23c031 Tejun Heo 2013-11-28 449 goto out_put;
414985ae23c031 Tejun Heo 2013-11-28 450
414985ae23c031 Tejun Heo 2013-11-28 451 rc = -EINVAL;
414985ae23c031 Tejun Heo 2013-11-28 452 if (of->mmapped && of->vm_ops != vma->vm_ops)
414985ae23c031 Tejun Heo 2013-11-28 453 goto out_put;
414985ae23c031 Tejun Heo 2013-11-28 454
414985ae23c031 Tejun Heo 2013-11-28 455 /*
414985ae23c031 Tejun Heo 2013-11-28 456 * It is not possible to successfully wrap close.
414985ae23c031 Tejun Heo 2013-11-28 457 * So error if someone is trying to use close.
414985ae23c031 Tejun Heo 2013-11-28 458 */
414985ae23c031 Tejun Heo 2013-11-28 @459 if (vma->vm_ops && vma->vm_ops->close)
^^^^^^^^^^^
If ->vm_ops is NULL
414985ae23c031 Tejun Heo 2013-11-28 460 goto out_put;
414985ae23c031 Tejun Heo 2013-11-28 461
927bb8d619fea4 Martin Oliveira 2024-06-11 @462 if (vma->vm_ops->page_mkwrite)
^^^^^^^^^^^^^^^^^^^^^^^^^
then we're in trouble
927bb8d619fea4 Martin Oliveira 2024-06-11 463 goto out_put;
927bb8d619fea4 Martin Oliveira 2024-06-11 464
414985ae23c031 Tejun Heo 2013-11-28 465 rc = 0;
05d8f255867e31 Neel Natu 2024-01-27 466 if (!of->mmapped) {
a1d82aff5df760 Tejun Heo 2016-12-27 467 of->mmapped = true;
bdb2fd7fc56e19 Tejun Heo 2022-08-27 468 of_on(of)->nr_mmapped++;
414985ae23c031 Tejun Heo 2013-11-28 469 of->vm_ops = vma->vm_ops;
05d8f255867e31 Neel Natu 2024-01-27 470 }
414985ae23c031 Tejun Heo 2013-11-28 471 vma->vm_ops = &kernfs_vm_ops;
414985ae23c031 Tejun Heo 2013-11-28 472 out_put:
c637b8acbe079e Tejun Heo 2013-12-11 473 kernfs_put_active(of->kn);
414985ae23c031 Tejun Heo 2013-11-28 474 out_unlock:
414985ae23c031 Tejun Heo 2013-11-28 475 mutex_unlock(&of->mutex);
414985ae23c031 Tejun Heo 2013-11-28 476
414985ae23c031 Tejun Heo 2013-11-28 477 return rc;
414985ae23c031 Tejun Heo 2013-11-28 478 }
On Tue, Jun 11, 2024 at 12:27:29PM -0600, Martin Oliveira wrote: > + if (vma->vm_ops->page_mkwrite) > + goto out_put; > + I'd probably make this a WARN_ON so that driver authors trying to add a page_mkwrite in the vm_ops passed to kernfs get a big fat warning instead of spending a couple hours trying to track down what is going wrong :)
On 6/11/24 11:27 AM, Martin Oliveira wrote: > The .page_mkwrite operator of kernfs just calls file_update_time(). > This is the same behaviour that the fault code does if .page_mkwrite is > not set. > > Furthermore, having the page_mkwrite() operator causes > writable_file_mapping_allowed() to fail due to > vma_needs_dirty_tracking() on the gup flow, which is a pre-requisite for > enabling P2PDMA over RDMA. > > There are no users of .page_mkwrite and no known valid use cases, so > just remove the .page_mkwrite from kernfs_ops and return -EINVAL if an > mmap() implementation sets .page_mkwrite. Hi Martin and Logan! First of all, I admire this approach to solving one of the gup+filesystem interaction problems, by coming in from the other direction. Neat. :) > > Co-developed-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com> > --- > fs/kernfs/file.c | 26 +++----------------------- > 1 file changed, 3 insertions(+), 23 deletions(-) > > diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c > index 8502ef68459b9..a198cb0718772 100644 > --- a/fs/kernfs/file.c > +++ b/fs/kernfs/file.c > @@ -386,28 +386,6 @@ static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf) > return ret; > } > > -static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf) > -{ > - struct file *file = vmf->vma->vm_file; > - struct kernfs_open_file *of = kernfs_of(file); > - vm_fault_t ret; > - > - if (!of->vm_ops) > - return VM_FAULT_SIGBUS; > - > - if (!kernfs_get_active(of->kn)) > - return VM_FAULT_SIGBUS; > - > - ret = 0; > - if (of->vm_ops->page_mkwrite) > - ret = of->vm_ops->page_mkwrite(vmf); > - else > - file_update_time(file); > - > - kernfs_put_active(of->kn); > - return ret; > -} > - > static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr, > void *buf, int len, int write) > { > @@ -432,7 +410,6 @@ static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr, > static const struct vm_operations_struct kernfs_vm_ops = { > .open = kernfs_vma_open, > .fault = kernfs_vma_fault, > - .page_mkwrite = kernfs_vma_page_mkwrite, > .access = kernfs_vma_access, > }; > > @@ -482,6 +459,9 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma) > if (vma->vm_ops && vma->vm_ops->close) > goto out_put; > > + if (vma->vm_ops->page_mkwrite) As the kernel test bot results imply, you probably want to do it like this: if (vma->vm_ops && vma->vm_ops->page_mkwrite) > + goto out_put; > + > rc = 0; > if (!of->mmapped) { > of->mmapped = true; thanks,
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 8502ef68459b9..a198cb0718772 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -386,28 +386,6 @@ static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf) return ret; } -static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf) -{ - struct file *file = vmf->vma->vm_file; - struct kernfs_open_file *of = kernfs_of(file); - vm_fault_t ret; - - if (!of->vm_ops) - return VM_FAULT_SIGBUS; - - if (!kernfs_get_active(of->kn)) - return VM_FAULT_SIGBUS; - - ret = 0; - if (of->vm_ops->page_mkwrite) - ret = of->vm_ops->page_mkwrite(vmf); - else - file_update_time(file); - - kernfs_put_active(of->kn); - return ret; -} - static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr, void *buf, int len, int write) { @@ -432,7 +410,6 @@ static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr, static const struct vm_operations_struct kernfs_vm_ops = { .open = kernfs_vma_open, .fault = kernfs_vma_fault, - .page_mkwrite = kernfs_vma_page_mkwrite, .access = kernfs_vma_access, }; @@ -482,6 +459,9 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma) if (vma->vm_ops && vma->vm_ops->close) goto out_put; + if (vma->vm_ops->page_mkwrite) + goto out_put; + rc = 0; if (!of->mmapped) { of->mmapped = true;