From: Jan Kara Date: Tue, 18 Aug 2009 02:17:20 +0000 (-0400) Subject: ext4: Fix possible deadlock between ext4_truncate() and ext4_get_blocks() X-Git-Tag: v2.6.32-rc1~633^2~45 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=487caeef9fc08c0565e082c40a8aaf58dad92bbb;p=pandora-kernel.git ext4: Fix possible deadlock between ext4_truncate() and ext4_get_blocks() During truncate we are sometimes forced to start a new transaction as the amount of blocks to be journaled is both quite large and hard to predict. So far we restarted a transaction while holding i_data_sem and that violates lock ordering because i_data_sem ranks below a transaction start (and it can lead to a real deadlock with ext4_get_blocks() mapping blocks in some page while having a transaction open). We fix the problem by dropping the i_data_sem before restarting the transaction and acquire it afterwards. It's slightly subtle that this works: 1) By the time ext4_truncate() is called, all the page cache for the truncated part of the file is dropped so get_block() should not be called on it (we only have to invalidate extent cache after we reacquire i_data_sem because some extent from not-truncated part could extend also into the part we are going to truncate). 2) Writes, migrate or defrag hold i_mutex so they are stopped for all the time of the truncate. This bug has been found and analyzed by Theodore Tso . Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- Reading git-diff-tree failed