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From: David Sterba <dsterba@suse.cz>
To: Nikolay Borisov <nborisov@suse.com>
Cc: dsterba@suse.cz, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v2] btrfs: Ensure replaced device doesn't have pending chunk allocation
Date: Fri, 17 May 2019 16:28:45 +0200
Message-ID: <20190517142845.GC3138@twin.jikos.cz> (raw)
In-Reply-To: <20190517074425.30072-1-nborisov@suse.com>

On Fri, May 17, 2019 at 10:44:25AM +0300, Nikolay Borisov wrote:
> Recent FITRIM work, namely bbbf7243d62d ("btrfs: combine device update
> operations during transaction commit") combined the way certain
> operations are recoded in a transaction. As a result an ASSERT was
> added in dev_replace_finish to ensure the new code works correctly.
> Unfortunately I got reports that it's possible to trigger the assert,
> meaning that during a device replace it's possible to have an unfinished
> chunk allocation on the source device.
> 
> This is supposed to be prevented by the fact that a transaction is
> committed before finishing the replace oepration and alter acquiring
> the chunk mutex. This is not sufficient since by the time the
> transaction is committed and the chunk mutex acquired it's possible to
> allocate a chunk depending on the workload being executed on the
> replaced device. This bug has been present ever since device replace was
> introduced but there was never code which checks for it.
> 
> The correct way to fix is to ensure that there is no pending device
> modification operation when the chunk mutex is acquire and if there is
> repeat transaction commit. Unfortunately it's not possible to just
> exclude the source device from btrfs_fs_devices::dev_alloc_list since
> this causes ENOSPC to be hit in transaction commit.
> 
> Fixes: 391cd9df81ac ("Btrfs: fix unprotected alloc list insertion during the finishing procedure of replace")
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>

Added to misc-next, thanks.

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-14 10:54 [PATCH 0/8] Misc improvements to dev-replace code Nikolay Borisov
2019-05-14 10:54 ` [PATCH 1/8] btrfs: Don't opencode sync_blockdev in btrfs_init_dev_replace_tgtdev Nikolay Borisov
2019-05-14 10:59   ` Johannes Thumshirn
2019-05-14 10:54 ` [PATCH 2/8] btrfs: Reduce critical section " Nikolay Borisov
2019-05-14 11:05   ` Johannes Thumshirn
2019-05-14 10:54 ` [PATCH 3/8] btrfs: Remove impossible WARN_ON Nikolay Borisov
2019-05-14 11:09   ` Johannes Thumshirn
2019-05-14 10:54 ` [PATCH 4/8] btrfs: Ensure btrfs_init_dev_replace_tgtdev sees up to date values Nikolay Borisov
2019-05-14 10:54 ` [PATCH 5/8] btrfs: Streamline replace sem unlock in btrfs_dev_replace_start Nikolay Borisov
2019-05-14 12:50   ` Johannes Thumshirn
2019-05-14 10:54 ` [PATCH 6/8] btrfs: Explicitly reserve space for devreplace item Nikolay Borisov
2019-05-14 12:56   ` Johannes Thumshirn
2019-05-14 10:54 ` [PATCH 7/8] btrfs: Ensure replaced device doesn't have pending chunk allocation Nikolay Borisov
2019-05-15 16:52   ` David Sterba
2019-05-17  7:44     ` [PATCH v2] " Nikolay Borisov
2019-05-17 14:28       ` David Sterba [this message]
2019-05-14 10:54 ` [PATCH 8/8] btrfs: Remove redundant assignment of tgt_device->commit_total_bytes Nikolay Borisov
2019-05-14 12:59   ` Johannes Thumshirn

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