btrfs: add memalloc_nofs protections around alloc_workspace callback (fe308533) · Commits · 戴 / test

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>

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 @@ 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);

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