linux-kernel - Re: [PATCH 1/2] block: shutdown blktrace in case of fatal signal pending

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Message-ID: <YGgi6FOr6cEiei+7@T590>
Date:   Sat, 3 Apr 2021 16:10:16 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] block: shutdown blktrace in case of fatal signal
 pending

On Fri, Apr 02, 2021 at 07:27:30PM +0200, Christoph Hellwig wrote:
> On Wed, Mar 31, 2021 at 08:16:50AM +0800, Ming Lei wrote:
> > On Tue, Mar 30, 2021 at 06:53:30PM +0200, Christoph Hellwig wrote:
> > > On Tue, Mar 23, 2021 at 04:14:39PM +0800, Ming Lei wrote:
> > > > blktrace may allocate lots of memory, if the process is terminated
> > > > by user or OOM, we need to provide one chance to remove the trace
> > > > buffer, otherwise memory leak may be caused.
> > > > 
> > > > Fix the issue by shutdown blktrace in case of task exiting in
> > > > blkdev_close().
> > > > 
> > > > Signed-off-by: Ming Lei <ming.lei@...hat.com>
> > > 
> > > This just seems weird.  blktrace has no relationship to open
> > > block device instances.
> > 
> > blktrace still needs to open one blkdev, then send its own ioctl
> > commands to block layer. In case of OOM, the allocated memory in
> > these ioctl commands won't be released.
> > 
> > Or any other suggestion?
> 
> Not much we can do there I think.  If we want to autorelease memory
> it needs to be an API that ties the memory allocation to an FD.

We still may shutdown blktrace if current is the last opener, otherwise
new blktrace can't be started and memory should be leaked forever, and
what do you think of the revised version?

>From de33ec85ee1ce2865aa04f2639e480ea4db4eebf Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@...hat.com>
Date: Tue, 23 Mar 2021 10:32:23 +0800
Subject: [PATCH] block: shutdown blktrace in case of task exiting

blktrace may allocate lots of memory, if the process is terminated
by user or OOM, we need to provide one chance to remove the trace
buffer, otherwise memory leak may be caused. Also new blktrace
instance can't be started too.

Fix the issue by shutdown blktrace in case of task exiting in
blkdev_close() when it is the last opener.

Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 fs/block_dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 92ed7d5df677..8fa59cecce72 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -34,6 +34,7 @@
 #include <linux/part_stat.h>
 #include <linux/uaccess.h>
 #include <linux/suspend.h>
+#include <linux/blktrace_api.h>
 #include "internal.h"
 
 struct bdev_inode {
@@ -1646,6 +1647,11 @@ EXPORT_SYMBOL(blkdev_put);
 static int blkdev_close(struct inode * inode, struct file * filp)
 {
 	struct block_device *bdev = I_BDEV(bdev_file_inode(filp));
+
+	/* shutdown blktrace in case of exiting which may be from OOM */
+	if ((current->flags & PF_EXITING) && (bdev->bd_openers == 1))
+		blk_trace_shutdown(bdev->bd_disk->queue);
+
 	blkdev_put(bdev, filp->f_mode);
 	return 0;
 }
-- 
2.29.2


-- 
Ming