Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit fe308533 authored by David Sterba's avatar David Sterba
Browse files

btrfs: add memalloc_nofs protections around alloc_workspace callback 



The workspaces are preallocated at the beginning where we can safely use
GFP_KERNEL, but in some cases the find_workspace might reach the
allocation again, now in a more restricted context when the bios or
pages are being compressed.

To avoid potential lockup when alloc_workspace -> vmalloc would silently
use the GFP_KERNEL, add the memalloc_nofs helpers around the critical
call site.

Reviewed-by: default avatarAnand Jain <anand.jain@oracle.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent adf02123

fs/btrfs/compression.c

+10 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 
#include <linux/writeback.h>

#include <linux/bit_spinlock.h>

#include <linux/slab.h>

#include <linux/sched/mm.h>

#include "ctree.h"

#include "disk-io.h"

#include "transaction.h"
@@ -757,6 +758,7 @@ static struct list_head *find_workspace(int type) 
	struct list_head *workspace;

	int cpus = num_online_cpus();

	int idx = type - 1;

	unsigned nofs_flag;



	struct list_head *idle_ws	= &btrfs_comp_ws[idx].idle_ws;

	spinlock_t *ws_lock		= &btrfs_comp_ws[idx].ws_lock;
@@ -786,7 +788,15 @@ static struct list_head *find_workspace(int type) 
	atomic_inc(total_ws);

	spin_unlock(ws_lock);



	/*

	 * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have

	 * to turn it off here because we might get called from the restricted

	 * context of btrfs_compress_bio/btrfs_compress_pages

	 */

	nofs_flag = memalloc_nofs_save();

	workspace = btrfs_compress_op[idx]->alloc_workspace();

	memalloc_nofs_restore(nofs_flag);



	if (IS_ERR(workspace)) {

		atomic_dec(total_ws);

		wake_up(ws_wait);