LKML Archive on
help / color / mirror / Atom feed
From: Desmond Cheong Zhi Xi <>
Cc: Desmond Cheong Zhi Xi <>,,,,,,,
Subject: [PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids
Date: Tue, 27 Jul 2021 15:13:03 +0800	[thread overview]
Message-ID: <> (raw)

When removing a writeable device in __btrfs_free_extra_devids, the rw
device count should be decremented.

This error was caught by Syzbot which reported a warning in
close_fs_devices because fs_devices->rw_devices was not 0 after
closing all devices. Here is the call trace that was observed:

      device_list_add();   <---------------- device added
        btrfs_open_one_device();   <-------- writable device opened,
	                                     rw device count ++
	  __btrfs_free_extra_devids();  <--- writable device removed,
	                              rw device count not decremented
	      close_fs_devices();   <------- rw device count off by 1

As a note, prior to commit cf89af146b7e ("btrfs: dev-replace: fail
mount if we don't have replace item with target device"), rw_devices
was decremented on removing a writable device in
__btrfs_free_extra_devids only if the BTRFS_DEV_STATE_REPLACE_TGT bit
was not set for the device. However, this check does not need to be
reinstated as it is now redundant and incorrect.

In __btrfs_free_extra_devids, we skip removing the device if it is the
target for replacement. This is done by checking whether device->devid
only on the device with devid BTRFS_DEV_REPLACE_DEVID, no devices
should have the BTRFS_DEV_STATE_REPLACE_TGT bit set after the check,
and so it's redundant to test for that bit.

Additionally, following commit 82372bc816d7 ("Btrfs: make
the logic of source device removing more clear"), rw_devices is
incremented whenever a writeable device is added to the alloc
list (including the target device in btrfs_dev_replace_finishing), so
all removals of writable devices from the alloc list should also be
accompanied by a decrement to rw_devices.

Fixes: cf89af146b7e ("btrfs: dev-replace: fail mount if we don't have replace item with target device")
Signed-off-by: Desmond Cheong Zhi Xi <>
Reviewed-by: Anand Jain <>
 fs/btrfs/volumes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 807502cd6510..916c25371658 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1078,6 +1078,7 @@ static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices,
 		if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
 			clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+			fs_devices->rw_devices--;

             reply	other threads:[~2021-07-27  7:13 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27  7:13 Desmond Cheong Zhi Xi [this message]
2021-07-28 12:58 ` David Sterba
2021-08-12 10:38 ` David Sterba
2021-08-12 15:43   ` Desmond Cheong Zhi Xi
2021-08-12 15:50     ` David Sterba
2021-08-12 17:31       ` Desmond Cheong Zhi Xi
2021-08-13  8:51         ` David Sterba
2021-08-13  9:57           ` Desmond Cheong Zhi Xi
2021-08-13 10:30             ` David Sterba
2021-08-19 17:11               ` Desmond Cheong Zhi Xi
2021-08-19 17:34                 ` David Sterba
2021-08-20  3:09                   ` Desmond Cheong Zhi Xi
2021-08-20 10:58                     ` David Sterba
2021-08-20 17:53                       ` Desmond Cheong Zhi Xi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \
    --subject='Re: [PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).