Patch "UBIFS: fix an mmap and fsync race condition" has been added to the 3.10-stable tree

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This is a note to let you know that I've just added the patch titled

    UBIFS: fix an mmap and fsync race condition

to the 3.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ubifs-fix-an-mmap-and-fsync-race-condition.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 691a7c6f28ac90cccd0dbcf81348ea90b211bdd0 Mon Sep 17 00:00:00 2001
From: hujianyang <hujianyang@xxxxxxxxxx>
Date: Wed, 30 Apr 2014 14:06:06 +0800
Subject: UBIFS: fix an mmap and fsync race condition

From: hujianyang <hujianyang@xxxxxxxxxx>

commit 691a7c6f28ac90cccd0dbcf81348ea90b211bdd0 upstream.

There is a race condition in UBIFS:

Thread A (mmap)                        Thread B (fsync)

->__do_fault                           ->write_cache_pages
   -> ubifs_vm_page_mkwrite
       -> budget_space
       -> lock_page
       -> release/convert_page_budget
       -> SetPagePrivate
       -> TestSetPageDirty
       -> unlock_page
                                       -> lock_page
                                           -> TestClearPageDirty
                                           -> ubifs_writepage
                                               -> do_writepage
                                                   -> release_budget
                                                   -> ClearPagePrivate
                                                   -> unlock_page
   -> !(ret & VM_FAULT_LOCKED)
   -> lock_page
   -> set_page_dirty
       -> ubifs_set_page_dirty
           -> TestSetPageDirty (set page dirty without budgeting)
   -> unlock_page

This leads to situation where we have a diry page but no budget allocated for
this page, so further write-back may fail with -ENOSPC.

In this fix we return from page_mkwrite without performing unlock_page. We
return VM_FAULT_LOCKED instead. After doing this, the race above will not
happen.

Signed-off-by: hujianyang <hujianyang@xxxxxxxxxx>
Tested-by: Laurence Withers <lwithers@xxxxxxxxxx>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/ubifs/file.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1524,8 +1524,7 @@ static int ubifs_vm_page_mkwrite(struct
 	}
 
 	wait_for_stable_page(page);
-	unlock_page(page);
-	return 0;
+	return VM_FAULT_LOCKED;
 
 out_unlock:
 	unlock_page(page);


Patches currently in stable-queue which might be from hujianyang@xxxxxxxxxx are

queue-3.10/ubifs-remove-incorrect-assertion-in-shrink_tnc.patch
queue-3.10/ubifs-fix-an-mmap-and-fsync-race-condition.patch
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