[PATCH 6/9] jbd2: mark the transaction context with the scope GFP_NOFS context

[Michal Hocko]

From: Michal Hocko <mho...@suse.com>

now that we have memalloc_nofs_{save,restore} api we can mark the whole
transaction context as implicitly GFP_NOFS. All allocations will
automatically inherit GFP_NOFS this way. This means that we do not have
to mark any of those requests with GFP_NOFS and moreover all the
ext4_kv[mz]alloc(GFP_NOFS) are also safe now because even the hardcoded
GFP_KERNEL allocations deep inside the vmalloc will be NOFS now.

Signed-off-by: Michal Hocko <mho...@suse.com>
---
 fs/jbd2/transaction.c | 11 +++++++++++
 include/linux/jbd2.h  |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e1652665bd93..35a5d3d76182 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -388,6 +388,11 @@ static int start_this_handle(journal_t *journal, handle_t 
*handle,
 
        rwsem_acquire_read(&journal->j_trans_commit_map, 0, 0, _THIS_IP_);
        jbd2_journal_free_transaction(new_transaction);
+       /*
+        * Make sure that no allocations done while the transaction is
+        * open is going to recurse back to the fs layer.
+        */
+       handle->saved_alloc_context = memalloc_nofs_save();
        return 0;
 }
 
@@ -466,6 +471,7 @@ handle_t *jbd2__journal_start(journal_t *journal, int 
nblocks, int rsv_blocks,
        trace_jbd2_handle_start(journal->j_fs_dev->bd_dev,
                                handle->h_transaction->t_tid, type,
                                line_no, nblocks);
+
        return handle;
 }
 EXPORT_SYMBOL(jbd2__journal_start);
@@ -1760,6 +1766,11 @@ int jbd2_journal_stop(handle_t *handle)
        if (handle->h_rsv_handle)
                jbd2_journal_free_reserved(handle->h_rsv_handle);
 free_and_exit:
+       /*
+        * scope of th GFP_NOFS context is over here and so we can
+        * restore the original alloc context.
+        */
+       memalloc_nofs_restore(handle->saved_alloc_context);
        jbd2_free_handle(handle);
        return err;
 }
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index dfaa1f4dcb0c..606b6bce3a5b 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -491,6 +491,8 @@ struct jbd2_journal_handle
 
        unsigned long           h_start_jiffies;
        unsigned int            h_requested_credits;
+
+       unsigned int            saved_alloc_context;
 };
 
 
-- 
2.10.2