From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: miklos@szeredi.hu, ktkhai@virtuozzo.com,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] fuse: Fix race in fuse_writepage_in_flight()
Date: Mon, 26 Nov 2018 12:46:10 +0300 [thread overview]
Message-ID: <154322517208.18737.3297786654135648324.stgit@localhost.localdomain> (raw)
Checking for FR_PENDING in fuse_writepage_in_flight() is racy.
It does not guarantee the first request in misc.write.next list
is not in userspace, since there we take fc->lock, while
fuse_dev_do_read() takes fiq->waitq.lock:
fuse_dev_read() fuse_writepage_in_flight()
test_bit(FR_PENDING)
clear_bit(FR_PENDING)
handle old_req->pages[0] in userspace
copy_highpage(old_req->pages[0], page)
^^^^^
userspace never sees this pages
The only reliable way to determ, whether we are able to replace
old_req's page, is to completely skip the first request in the list.
This patch makes the function to do that.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
fs/fuse/file.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b52f9baaa3e7..c6650c68b31a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1740,6 +1740,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
{
struct fuse_conn *fc = get_fuse_conn(new_req->inode);
struct fuse_inode *fi = get_fuse_inode(new_req->inode);
+ struct fuse_req *first_req;
struct fuse_req *tmp;
struct fuse_req *old_req;
bool found = false;
@@ -1764,6 +1765,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
}
new_req->num_pages = 1;
+ first_req = old_req;
for (tmp = old_req; tmp != NULL; tmp = tmp->misc.write.next) {
BUG_ON(tmp->inode != new_req->inode);
curr_index = tmp->misc.write.in.offset >> PAGE_SHIFT;
@@ -1773,7 +1775,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
}
}
- if (old_req->num_pages == 1 && test_bit(FR_PENDING, &old_req->flags)) {
+ if (old_req->num_pages == 1 && old_req != first_req) {
struct backing_dev_info *bdi = inode_to_bdi(page->mapping->host);
copy_highpage(old_req->pages[0], page);
next reply other threads:[~2018-11-26 9:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-26 9:46 Kirill Tkhai [this message]
2018-11-26 9:46 ` [PATCH 2/2] fuse: Replace page without copying in fuse_writepage_in_flight() Kirill Tkhai
2019-01-15 15:39 ` Miklos Szeredi
2019-01-15 16:14 ` Kirill Tkhai
2019-01-15 16:36 ` Miklos Szeredi
2019-01-15 16:38 ` Kirill Tkhai
2019-01-10 10:48 ` [PATCH 1/2] fuse: Fix race " Kirill Tkhai
2019-01-10 11:00 ` Miklos Szeredi
2019-01-10 11:03 ` Kirill Tkhai
2019-01-15 15:37 ` Miklos Szeredi
2019-01-15 15:55 ` Kirill Tkhai
2019-01-15 16:03 ` Miklos Szeredi
2019-01-15 16:05 ` Kirill Tkhai
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