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[PATCH v1 2/3] fs: Optimize credentials reference count for backing file ops

Vinicius Costa Gomes posted 3 patches 1 year, 10 months ago
There is a newer version of this series
[PATCH v1 2/3] fs: Optimize credentials reference count for backing file ops
Posted by Vinicius Costa Gomes 1 year, 10 months ago 
For backing file operations, users are expected to pass credentials
that will outlive the backing file common operations.

Use the specialized guard statements to override/revert the
credentials.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
---
 fs/backing-file.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/fs/backing-file.c b/fs/backing-file.c
index 740185198db3..9610d5166736 100644
--- a/fs/backing-file.c
+++ b/fs/backing-file.c
@@ -140,7 +140,6 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 			       struct backing_file_ctx *ctx)
 {
 	struct backing_aio *aio = NULL;
-	const struct cred *old_cred;
 	ssize_t ret;
 
 	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
@@ -153,7 +152,7 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 	    !(file->f_mode & FMODE_CAN_ODIRECT))
 		return -EINVAL;
 
-	old_cred = override_creds(ctx->cred);
+	cred_guard(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);
 
@@ -174,8 +173,6 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 			backing_aio_cleanup(aio, ret);
 	}
 out:
-	revert_creds(old_cred);
-
 	if (ctx->accessed)
 		ctx->accessed(ctx->user_file);
 
@@ -187,7 +184,6 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 				struct kiocb *iocb, int flags,
 				struct backing_file_ctx *ctx)
 {
-	const struct cred *old_cred;
 	ssize_t ret;
 
 	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
@@ -210,7 +206,7 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 	 */
 	flags &= ~IOCB_DIO_CALLER_COMP;
 
-	old_cred = override_creds(ctx->cred);
+	cred_guard(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);
 
@@ -222,12 +218,12 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 
 		ret = backing_aio_init_wq(iocb);
 		if (ret)
-			goto out;
+			return ret;
 
 		ret = -ENOMEM;
 		aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 		if (!aio)
-			goto out;
+			return ret;
 
 		aio->orig_iocb = iocb;
 		aio->end_write = ctx->end_write;
@@ -240,9 +236,6 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 		if (ret != -EIOCBQUEUED)
 			backing_aio_cleanup(aio, ret);
 	}
-out:
-	revert_creds(old_cred);
-
 	return ret;
 }
 EXPORT_SYMBOL_GPL(backing_file_write_iter);
@@ -252,15 +245,13 @@ ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
 				 unsigned int flags,
 				 struct backing_file_ctx *ctx)
 {
-	const struct cred *old_cred;
 	ssize_t ret;
 
 	if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
 		return -EIO;
 
-	old_cred = override_creds(ctx->cred);
+	cred_guard(ctx->cred);
 	ret = vfs_splice_read(in, ppos, pipe, len, flags);
-	revert_creds(old_cred);
 
 	if (ctx->accessed)
 		ctx->accessed(ctx->user_file);
@@ -274,7 +265,6 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
 				  unsigned int flags,
 				  struct backing_file_ctx *ctx)
 {
-	const struct cred *old_cred;
 	ssize_t ret;
 
 	if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
@@ -284,11 +274,10 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
 	if (ret)
 		return ret;
 
-	old_cred = override_creds(ctx->cred);
+	cred_guard(ctx->cred);
 	file_start_write(out);
 	ret = iter_file_splice_write(pipe, out, ppos, len, flags);
 	file_end_write(out);
-	revert_creds(old_cred);
 
 	if (ctx->end_write)
 		ctx->end_write(ctx->user_file);
@@ -300,7 +289,6 @@ EXPORT_SYMBOL_GPL(backing_file_splice_write);
 int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
 		      struct backing_file_ctx *ctx)
 {
-	const struct cred *old_cred;
 	int ret;
 
 	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
@@ -312,9 +300,8 @@ int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
 
 	vma_set_file(vma, file);
 
-	old_cred = override_creds(ctx->cred);
+	cred_guard(ctx->cred);
 	ret = call_mmap(vma->vm_file, vma);
-	revert_creds(old_cred);
 
 	if (ctx->accessed)
 		ctx->accessed(ctx->user_file);
-- 
2.44.0
Re: [PATCH v1 2/3] fs: Optimize credentials reference count for backing file ops
Posted by kernel test robot 1 year, 10 months ago 
Hi Vinicius,

kernel test robot noticed the following build warnings:

[auto build test WARNING on brauner-vfs/vfs.all]
[also build test WARNING on linus/master v6.9-rc2 next-20240403]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Vinicius-Costa-Gomes/cred-Add-a-light-version-of-override-revert_creds/20240403-101954
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.all
patch link:    https://lore.kernel.org/r/20240403021808.309900-3-vinicius.gomes%40intel.com
patch subject: [PATCH v1 2/3] fs: Optimize credentials reference count for backing file ops
config: i386-randconfig-061-20240403 (https://download.01.org/0day-ci/archive/20240403/202404032344.SKdrnkhI-lkp@intel.com/config)
compiler: gcc-13 (Ubuntu 13.2.0-4ubuntu3) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240403/202404032344.SKdrnkhI-lkp@intel.com/reproduce)

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>
| Closes: https://lore.kernel.org/oe-kbuild-all/202404032344.SKdrnkhI-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   fs/backing-file.c: note: in included file (through include/linux/sched/signal.h, include/linux/rcuwait.h, include/linux/percpu-rwsem.h, ...):
>> include/linux/cred.h:182:41: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct cred const *old @@     got struct cred const [noderef] __rcu *cred @@
   include/linux/cred.h:182:41: sparse:     expected struct cred const *old
   include/linux/cred.h:182:41: sparse:     got struct cred const [noderef] __rcu *cred
>> include/linux/cred.h:182:41: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct cred const *old @@     got struct cred const [noderef] __rcu *cred @@
   include/linux/cred.h:182:41: sparse:     expected struct cred const *old
   include/linux/cred.h:182:41: sparse:     got struct cred const [noderef] __rcu *cred
>> include/linux/cred.h:182:41: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct cred const *old @@     got struct cred const [noderef] __rcu *cred @@
   include/linux/cred.h:182:41: sparse:     expected struct cred const *old
   include/linux/cred.h:182:41: sparse:     got struct cred const [noderef] __rcu *cred
>> include/linux/cred.h:182:41: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct cred const *old @@     got struct cred const [noderef] __rcu *cred @@
   include/linux/cred.h:182:41: sparse:     expected struct cred const *old
   include/linux/cred.h:182:41: sparse:     got struct cred const [noderef] __rcu *cred
>> include/linux/cred.h:182:41: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct cred const *old @@     got struct cred const [noderef] __rcu *cred @@
   include/linux/cred.h:182:41: sparse:     expected struct cred const *old
   include/linux/cred.h:182:41: sparse:     got struct cred const [noderef] __rcu *cred

vim +182 include/linux/cred.h

58319057b78476 Andy Lutomirski      2015-09-04  174  
dd60a254548056 Vinicius Costa Gomes 2024-04-02  175  /*
dd60a254548056 Vinicius Costa Gomes 2024-04-02  176   * Override creds without bumping reference count. Caller must ensure
dd60a254548056 Vinicius Costa Gomes 2024-04-02  177   * reference remains valid or has taken reference. Almost always not the
dd60a254548056 Vinicius Costa Gomes 2024-04-02  178   * interface you want. Use override_creds()/revert_creds() instead.
dd60a254548056 Vinicius Costa Gomes 2024-04-02  179   */
dd60a254548056 Vinicius Costa Gomes 2024-04-02  180  static inline const struct cred *override_creds_light(const struct cred *override_cred)
dd60a254548056 Vinicius Costa Gomes 2024-04-02  181  {
dd60a254548056 Vinicius Costa Gomes 2024-04-02 @182  	const struct cred *old = current->cred;
dd60a254548056 Vinicius Costa Gomes 2024-04-02  183  
dd60a254548056 Vinicius Costa Gomes 2024-04-02  184  	rcu_assign_pointer(current->cred, override_cred);
dd60a254548056 Vinicius Costa Gomes 2024-04-02  185  	return old;
dd60a254548056 Vinicius Costa Gomes 2024-04-02  186  }
dd60a254548056 Vinicius Costa Gomes 2024-04-02  187  

-- 
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