From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zheng Liu Subject: Re: [PATCH 3/3] ext4: Fix deadlock when writing in ENOSPC conditions Date: Thu, 12 Dec 2013 14:51:16 +0800 Message-ID: <20131212065116.GB16199@gmail.com> References: <1386670440-3158-1-git-send-email-jack@suse.cz> <1386670440-3158-4-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ted Tso , Akira Fujita , linux-ext4@vger.kernel.org To: Jan Kara Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:54388 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751346Ab3LLGsI (ORCPT ); Thu, 12 Dec 2013 01:48:08 -0500 Received: by mail-pb0-f46.google.com with SMTP id md12so11370719pbc.5 for ; Wed, 11 Dec 2013 22:48:08 -0800 (PST) Content-Disposition: inline In-Reply-To: <1386670440-3158-4-git-send-email-jack@suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Dec 10, 2013 at 11:14:00AM +0100, Jan Kara wrote: > Akira-san has been reporting rare deadlocks of his machine when running > xfstests test 269 on ext4 filesystem. The problem turned out to be in > ext4_da_reserve_metadata() and ext4_da_reserve_space() which called > ext4_should_retry_alloc() while holding i_data_sem. Since > ext4_should_retry_alloc() can force a transaction commit, this is a > lock ordering violation and leads to deadlocks. > > Fix the problem by just removing the retry loops. These functions should > just report ENOSPC to the caller (e.g. ext4_da_write_begin()) and that > function must take care of retrying after dropping all necessary locks. > > Reported-and-tested-by: Akira Fujita > Signed-off-by: Jan Kara Thanks for fixing this. The patch looks good to me. You can add: Reviewed-by: Zheng Liu BTW, I have met a deadlock which is caused by ext4_da_reserve_space() in our product system. The calltrace information looks like this. So I want to make sure it is the root cause. But I couldn't reproduce the problem with running xfstest #269. Could you please tell me how to reproduce the deadlock? FWIW, I think we should backport this patch to stable kernel. Thanks, - Zheng > --- > fs/ext4/inode.c | 12 ------------ > 1 file changed, 12 deletions(-) > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 075763474118..61d49ff22c81 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -1206,7 +1206,6 @@ static int ext4_journalled_write_end(struct file *file, > */ > static int ext4_da_reserve_metadata(struct inode *inode, ext4_lblk_t lblock) > { > - int retries = 0; > struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); > struct ext4_inode_info *ei = EXT4_I(inode); > unsigned int md_needed; > @@ -1218,7 +1217,6 @@ static int ext4_da_reserve_metadata(struct inode *inode, ext4_lblk_t lblock) > * in order to allocate nrblocks > * worse case is one extent per block > */ > -repeat: > spin_lock(&ei->i_block_reservation_lock); > /* > * ext4_calc_metadata_amount() has side effects, which we have > @@ -1238,10 +1236,6 @@ repeat: > ei->i_da_metadata_calc_len = save_len; > ei->i_da_metadata_calc_last_lblock = save_last_lblock; > spin_unlock(&ei->i_block_reservation_lock); > - if (ext4_should_retry_alloc(inode->i_sb, &retries)) { > - cond_resched(); > - goto repeat; > - } > return -ENOSPC; > } > ei->i_reserved_meta_blocks += md_needed; > @@ -1255,7 +1249,6 @@ repeat: > */ > static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock) > { > - int retries = 0; > struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); > struct ext4_inode_info *ei = EXT4_I(inode); > unsigned int md_needed; > @@ -1277,7 +1270,6 @@ static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock) > * in order to allocate nrblocks > * worse case is one extent per block > */ > -repeat: > spin_lock(&ei->i_block_reservation_lock); > /* > * ext4_calc_metadata_amount() has side effects, which we have > @@ -1297,10 +1289,6 @@ repeat: > ei->i_da_metadata_calc_len = save_len; > ei->i_da_metadata_calc_last_lblock = save_last_lblock; > spin_unlock(&ei->i_block_reservation_lock); > - if (ext4_should_retry_alloc(inode->i_sb, &retries)) { > - cond_resched(); > - goto repeat; > - } > dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1)); > return -ENOSPC; > } > -- > 1.8.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html