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Message-ID: <CAMBkX3e_jyTZ=i8D8_cza23Xygd+Gf5iACZ+hbo5TaYLrJPH-Q@mail.gmail.com> Date: Tue, 10 Jan 2012 16:13:46 -0800 From: Surbhi Palande <csurbhi@...il.com> To: Jan Kara <jack@...e.cz> Cc: Eric Sandeen <sandeen@...deen.net>, Kamal Mostafa <kamal@...onical.com>, Alexander Viro <viro@...iv.linux.org.uk>, Andreas Dilger <adilger.kernel@...ger.ca>, Matthew Wilcox <matthew@....cx>, Randy Dunlap <rdunlap@...otime.net>, Theodore Tso <tytso@....edu>, linux-doc@...r.kernel.org, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, Valerie Aurora <val@...consulting.com>, Christopher Chaltain <christopher.chaltain@...onical.com>, "Peter M. Petrakis" <peter.petrakis@...onical.com>, Mikulas Patocka <mpatocka@...hat.com>, Surbhi Palande <surbhi.palande@...onical.com> Subject: Re: [PATCH v2 1/7] Adding support to freeze and unfreeze a journal Hi Jan, >> >> >> If all the write operations were journaled, then this patch would not allow >> ext4 filesystem to have any dirty data after its frozen. >> (as journal_start() would block). >> >> I think the only one candidate that creates dirty data without calling >> ext4_journal_start() is mmapped? > No, the problem is in any write path. The problem is with operations > that happen during the phase when s_frozen == SB_FREEZE_WRITE. These > operations dirty the filesystem but running sync may easily miss them. > During this phase journal is not frozen so that does not help you in any > way. > > Honza Ok! No new transaction can really start after the journal is frozen. But we can have dirty data after SB_FREEZE_WRITE and before SB_FREEZE_TRANS. I agree with you. However, can this be fixed by adding a sync_filesystem() in freeze_super() after the sb->s_op->freeze_fs() is over? So then essentially, when freeze_super() returns, the page cache is clean? I do definitely agree that the fix is to add a lock for mutual exclusion between freeze filesystem and writes to a frozen filesystem. Thanks! Regards, Surbhi. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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