linux-kernel - Re: [PATCH REVIEW] udf: Fix lock inversion between iprune_mutex and alloc

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Message-Id: <200808142048.10966.ioe-lkml@rameria.de>
Date:	Thu, 14 Aug 2008 20:48:10 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH REVIEW] udf: Fix lock inversion between iprune_mutex and alloc_mutex

Hi Jan,

On Thursday 14 August 2008, Jan Kara wrote:
> A memory allocation inside alloc_mutex must not recurse back
> into the filesystem itself because that leads to lock inversion
> between iprune_mutex and alloc_mutex (and thus to deadlocks - see
> traces below). Make allocations inside alloc_mutex use GFP_NOFS
> to avoid this problem.

What about moving the allocation before taking the mutex?
That way, we even reduce the lock contention and simplify the failure path.

Signed-off-by: Ingo Oeser <ioe-lkml@...eria.de>

diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
index eb9cfa2..76446eb 100644
--- a/fs/udf/ialloc.c
+++ b/fs/udf/ialloc.c
@@ -90,6 +90,25 @@ struct inode *udf_new_inode(struct inode *dir, int mode, int *err)
 		return NULL;
 	}
 
+	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
+		iinfo->i_efe = 1;
+		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
+			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
+		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
+					    sizeof(struct extendedFileEntry),
+					    GFP_KERNEL);
+	} else {
+		iinfo->i_efe = 0;
+		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
+					    sizeof(struct fileEntry),
+					    GFP_KERNEL);
+	}
+	if (!iinfo->i_ext.i_data) {
+		iput(inode);
+		*err = -ENOMEM;
+		return NULL;
+	}
+
 	mutex_lock(&sbi->s_alloc_mutex);
 	if (sbi->s_lvid_bh) {
 		struct logicalVolIntegrityDesc *lvid =
@@ -129,25 +148,6 @@ struct inode *udf_new_inode(struct inode *dir, int mode, int *err)
 	iinfo->i_lenEAttr = 0;
 	iinfo->i_lenAlloc = 0;
 	iinfo->i_use = 0;
-	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
-		iinfo->i_efe = 1;
-		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
-			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
-		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
-					    sizeof(struct extendedFileEntry),
-					    GFP_KERNEL);
-	} else {
-		iinfo->i_efe = 0;
-		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
-					    sizeof(struct fileEntry),
-					    GFP_KERNEL);
-	}
-	if (!iinfo->i_ext.i_data) {
-		iput(inode);
-		*err = -ENOMEM;
-		mutex_unlock(&sbi->s_alloc_mutex);
-		return NULL;
-	}
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
 		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
 	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
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