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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: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2017-05-31 17:14:56 +02:00
parent adf0212396
commit fe30853307
1 changed files with 10 additions and 0 deletions
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10
fs/btrfs/compression.c
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@ -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 @@ again:
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);