Re: [PATCH 3/5] btrfs: scrub: add memalloc_nofs protection around init_ipath

[Anand Jain]

On 06/01/17 01:49, David Sterba wrote:

init_ipath is called from a safe ioctl context and from scrub when
printing an error.  The protection is added for three reasons:

* init_data_container calls vmalloc and this does not work as expected
  in the GFP_NOFS context, so this silently does GFP_KERNEL and might
  deadlock in some cases
* keep the context constraint of GFP_NOFS, used by scrub
* we want to use GFP_KERNEL unconditionally inside init_ipath or its
  callees


 Reviewed-by: Anand Jain 

Thanks, Anand



Signed-off-by: David Sterba 
---
 fs/btrfs/scrub.c | 9 +
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index e99be644b19f..096e503e3ddc 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -18,6 +18,7 @@

 #include 
 #include 
+#include 
 #include "ctree.h"
 #include "volumes.h"
 #include "disk-io.h"
@@ -733,6 +734,7 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, 
u64 root,
u32 nlink;
int ret;
int i;
+   unsigned nofs_flag;
struct extent_buffer *eb;
struct btrfs_inode_item *inode_item;
struct scrub_warning *swarn = warn_ctx;
@@ -771,7 +773,14 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, 
u64 root,
nlink = btrfs_inode_nlink(eb, inode_item);
btrfs_release_path(swarn->path);

+   /*
+* init_path might indirectly call vmalloc, or use GFP_KERNEL. Scrub
+* uses GFP_NOFS in this context, so we keep it consistent but it does
+* not seem to be strictly necessary.
+*/
+   nofs_flag = memalloc_nofs_save();
ipath = init_ipath(4096, local_root, swarn->path);
+   memalloc_nofs_restore(nofs_flag);
if (IS_ERR(ipath)) {
ret = PTR_ERR(ipath);
ipath = NULL;


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[PATCH 3/5] btrfs: scrub: add memalloc_nofs protection around init_ipath

[David Sterba]

init_ipath is called from a safe ioctl context and from scrub when
printing an error.  The protection is added for three reasons:

* init_data_container calls vmalloc and this does not work as expected
  in the GFP_NOFS context, so this silently does GFP_KERNEL and might
  deadlock in some cases
* keep the context constraint of GFP_NOFS, used by scrub
* we want to use GFP_KERNEL unconditionally inside init_ipath or its
  callees

Signed-off-by: David Sterba 
---
 fs/btrfs/scrub.c | 9 +
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index e99be644b19f..096e503e3ddc 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -18,6 +18,7 @@
 
 #include 
 #include 
+#include 
 #include "ctree.h"
 #include "volumes.h"
 #include "disk-io.h"
@@ -733,6 +734,7 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, 
u64 root,
u32 nlink;
int ret;
int i;
+   unsigned nofs_flag;
struct extent_buffer *eb;
struct btrfs_inode_item *inode_item;
struct scrub_warning *swarn = warn_ctx;
@@ -771,7 +773,14 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, 
u64 root,
nlink = btrfs_inode_nlink(eb, inode_item);
btrfs_release_path(swarn->path);
 
+   /*
+* init_path might indirectly call vmalloc, or use GFP_KERNEL. Scrub
+* uses GFP_NOFS in this context, so we keep it consistent but it does
+* not seem to be strictly necessary.
+*/
+   nofs_flag = memalloc_nofs_save();
ipath = init_ipath(4096, local_root, swarn->path);
+   memalloc_nofs_restore(nofs_flag);
if (IS_ERR(ipath)) {
ret = PTR_ERR(ipath);
ipath = NULL;
-- 
2.12.0

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