Re: [PATCH] xfs: start inodegc after quota initialization

["Darrick J. Wong" <djwong@kernel.org>]

On Sun, Apr 12, 2026 at 09:49:25PM -0300, Pedro Demarchi Gomes wrote:
> When mounting a xfs filesystem with quotas, if an error occurs in xfs_mount
> after calling xfs_inodegc_start and before m_quotainfo initialization, the
> error path will call xfs_inodegc_flush assuming that m_quotainfo was already
> initialized, causing the following error:
> 
> [   82.411853][   T23] ==================================================================
> [   82.412678][   T23] BUG: KASAN: null-ptr-deref in mutex_lock (./include/linux/instrumented.h:55 ./include/linux/atomic/atomic-instrumented.h:4457 kernel/locking/mutex.c:159 kernel/locking/mutex.c:289)
> [   82.413383][   T23] Write of size 8 at addr 0000000000000030 by task kworker/1:0/23
> [   82.414187][   T23]
> [   82.414450][   T23] CPU: 1 UID: 0 PID: 23 Comm: kworker/1:0 Not tainted 7.0.0-rc5-00051-gbbeb83d3182a #35 PREEMPT(
> [   82.414458][   T23] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> [   82.414463][   T23] Workqueue: xfs-inodegc/loop0 xfs_inodegc_worker
> [   82.414478][   T23] Call Trace:
> [   82.414481][   T23]  <TASK>
> [   82.414484][   T23]  dump_stack_lvl (lib/dump_stack.c:122)
> [   82.414494][   T23]  print_report (mm/kasan/report.c:487)
> [   82.414518][   T23]  kasan_report (mm/kasan/report.c:597)
> [   82.414541][   T23]  kasan_check_range (mm/kasan/generic.c:? mm/kasan/generic.c:200)
> [   82.414549][   T23]  mutex_lock (./include/linux/instrumented.h:55 ./include/linux/atomic/atomic-instrumented.h:4457 kernel/locking/mutex.c:159 kernel/locking/mutex.c:289)
> [   82.414601][   T23]  xfs_qm_dqget_cache_lookup (fs/xfs/xfs_dquot.c:813)
> [   82.414609][   T23]  xfs_qm_dqget_inode (fs/xfs/xfs_dquot.c:1017)
> [   82.414678][   T23]  xfs_qm_dqattach_locked (fs/xfs/xfs_qm.c:331)
> [   82.414688][   T23]  xfs_qm_dqattach (fs/xfs/xfs_qm.c:371)
> [   82.414696][   T23]  xfs_inactive (fs/xfs/xfs_inode.c:1453)
> [   82.414733][   T23]  xfs_inodegc_worker (fs/xfs/xfs_icache.c:1946 fs/xfs/xfs_icache.c:1992)
> [   82.414743][   T23]  process_scheduled_works (kernel/workqueue.c:3281 kernel/workqueue.c:3359)
> [   82.414755][   T23]  worker_thread (kernel/workqueue.c:?)
> [   82.414775][   T23]  kthread (kernel/kthread.c:437)
> [   82.414787][   T23]  ret_from_fork (arch/x86/kernel/process.c:164)
> [   82.414822][   T23]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
> [   82.414834][   T23]  </TASK>
> 
> To avoid this, call xfs_inodegc_start after quota initialization.
> 
> Reported-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
> Closes: https://lore.kernel.org/all/DDC07F0C-05D2-46B4-9815-E010749FB3DC@gmail.com/
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
> ---
>  fs/xfs/xfs_mount.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index ef1ea8a1238c..d6f75ab41337 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -1057,7 +1057,6 @@ xfs_mountfs(
>  		xfs_clear_using_logged_xattrs(mp);
>  
>  	/* Enable background inode inactivation workers. */
> -	xfs_inodegc_start(mp);
>  	xfs_blockgc_start(mp);
>  
>  	if (xfs_has_metadir(mp)) {
> @@ -1143,6 +1142,8 @@ xfs_mountfs(
>  		}
>  	}
>  
> +	xfs_inodegc_start(mp);

Why is it correct to defer inodegc until this point?  Can any code
between line 1060 and 1145 push an inode to the inodegc mechanism?
blockgc can unmap blocks from files, so why is it ok to leave the
blockgc_start call where it is?

--D

> +
>  	/*
>  	 * Finish recovering the file system.  This part needed to be delayed
>  	 * until after the root and real-time bitmap inodes were consistently
> -- 
> 2.47.3
> 
>