[PATCH V2] fs: don't write pages when receiving a pending SIGKILL in __get_user_pages()

[PATCH V2] fs: don't write pages when receiving a pending SIGKILL in __get_user_pages()

[Xishi Qiu]

In the process IO direction, dio_refill_pages will call get_user_pages_fast 
to map the page from user space. If ret is less than 0 and IO is write, the 
function will create a zero page to fill data. This may work for some file 
system, but in some device operate we prefer whole write or fail, not half 
data half zero, e.g. fs metadata, like inode, identy.
This happens often when kill a process which is doing direct IO. Consider 
the following cases, the process A is doing IO process, may enter __get_user_pages 
function, if other processes send process A SIG_KILL, A will enter the 
following branches 
		/*
		 * If we have a pending SIGKILL, don't keep faulting
		 * pages and potentially allocating memory.
		 */
		if (unlikely(fatal_signal_pending(current)))
			return i ? i : -ERESTARTSYS;
Return current pages. direct IO will write the pages, the subsequent pages 
which can’t get will use zero page instead. 

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Signed-off-by: Bin Yang <robin.yb@huawei.com>
---
 fs/direct-io.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 0e04142..b74d565 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -174,6 +174,9 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
 		&dio->pages[0]);		/* Put results here */
 
 	if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
+		/* If task is killed, do not write anymore */
+		if (ret == -ERESTARTSYS)
+			goto out;
 		struct page *page = ZERO_PAGE(0);
 		/*
 		 * A memory fault, but the filesystem has some outstanding
-- 
1.7.1

Re: [PATCH V2] fs: don't write pages when receiving a pending SIGKILL in __get_user_pages()

[David Rientjes]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 2050 bytes --]

On Sat, 18 Jan 2014, Xishi Qiu wrote:

> In the process IO direction, dio_refill_pages will call get_user_pages_fast 
> to map the page from user space. If ret is less than 0 and IO is write, the 
> function will create a zero page to fill data. This may work for some file 
> system, but in some device operate we prefer whole write or fail, not half 
> data half zero, e.g. fs metadata, like inode, identy.

So you're attemping to define a behavior for all users of direct IO for a 
problem that is filesystem or backing device dependent?  Perhaps if you 
elaborated on the problem that you're seeing then we could address it.

> This happens often when kill a process which is doing direct IO. Consider 
> the following cases, the process A is doing IO process, may enter __get_user_pages 
> function, if other processes send process A SIG_KILL, A will enter the 
> following branches 
> 		/*
> 		 * If we have a pending SIGKILL, don't keep faulting
> 		 * pages and potentially allocating memory.
> 		 */
> 		if (unlikely(fatal_signal_pending(current)))
> 			return i ? i : -ERESTARTSYS;
> Return current pages. direct IO will write the pages, the subsequent pages 
> which can’t get will use zero page instead. 
> 
> Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
> Signed-off-by: Bin Yang <robin.yb@huawei.com>
> ---
>  fs/direct-io.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 0e04142..b74d565 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -174,6 +174,9 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
>  		&dio->pages[0]);		/* Put results here */
>  
>  	if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
> +		/* If task is killed, do not write anymore */
> +		if (ret == -ERESTARTSYS)
> +			goto out;
>  		struct page *page = ZERO_PAGE(0);
>  		/*
>  		 * A memory fault, but the filesystem has some outstanding

We don't mix declarations and text, please try to compile your patches 
before proposing them.