On 01/19/2019 02:07 AM, David Sterba wrote:
On Mon, Jan 14, 2019 at 04:21:43PM +0800, Anand Jain wrote:
On 01/12/2019 01:17 AM, fdmanana@xxxxxxxxxx wrote:
From: Filipe Manana <fdmanana@xxxxxxxx>
In a few places we are allocating a device using the GFP_KERNEL flag when
it is not safe to do so, because if reclaim is triggered it can cause a
transaction commit while we are holding the device list mutex. This mutex
is required in the transaction commit path (at write_all_supers() and
btrfs_update_commit_device_size()).
So fix this by setting up a nofs memory allocation context in those cases.
Fixes: 78f2c9e6dbb14 ("btrfs: device add and remove: use GFP_KERNEL")
Fixes: e0ae999414238 ("btrfs: preallocate device flush bio")
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
---
V2: Change the approach to fix the problem by setting up nofs contextes
where needed.
fs/btrfs/volumes.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2576b1a379c9..663566baae78 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -14,6 +14,7 @@
#include <linux/semaphore.h>
#include <linux/uuid.h>
#include <linux/list_sort.h>
+#include <linux/sched/mm.h>
#include "ctree.h"
#include "extent_map.h"
#include "disk-io.h"
@@ -988,20 +989,29 @@ static noinline struct btrfs_device *device_list_add(const char *path,
}
if (!device) {
+ unsigned int nofs_flag;
+
if (fs_devices->opened) {
mutex_unlock(&fs_devices->device_list_mutex);
return ERR_PTR(-EBUSY);
}
+ /*
+ * Setup nofs context because we are holding the device list
+ * mutex, which is required for a transaction commit.
+ */
I wonder if there is a bug due to GFP_KERNEL in device_list_add()?
as device_list_add() can only be called only when the FSID is not yet
mounted. OR if its done for the sake of consistency when calling\
btrfs_alloc_device().
It still could be called but a new device will not be allocated, all is
done either via scan or during mount. A missing device has an entry in
fs_devices.
We can keep th NOFS protection around that to make it future-proof, as
it's not trivial to see if this is always called from safe context or
not.
Makes sense to me.
Thanks.
