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.
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
---
fs/btrfs/compression.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index ba511dd454d5..39cd164e5a62 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -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);
--
2.12.0
--
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