Messages in this thread | | | Subject | Re: [PATCH v2 2/2] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim | From | Waiman Long <> | Date | Wed, 17 Jun 2020 21:35:59 -0400 |
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On 6/17/20 8:45 PM, Dave Chinner wrote: > On Wed, Jun 17, 2020 at 01:53:10PM -0400, Waiman Long wrote: >> fs/xfs/xfs_log.c | 9 +++++++++ >> fs/xfs/xfs_trans.c | 31 +++++++++++++++++++++++++++---- >> 2 files changed, 36 insertions(+), 4 deletions(-) >> >> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c >> index 00fda2e8e738..33244680d0d4 100644 >> --- a/fs/xfs/xfs_log.c >> +++ b/fs/xfs/xfs_log.c >> @@ -830,8 +830,17 @@ xlog_unmount_write( >> xfs_lsn_t lsn; >> uint flags = XLOG_UNMOUNT_TRANS; >> int error; >> + unsigned long pflags; >> >> + /* >> + * xfs_log_reserve() allocates memory. This can lead to fs reclaim >> + * which may conflicts with the unmount process. To avoid that, >> + * disable fs reclaim for this allocation. >> + */ >> + current_set_flags_nested(&pflags, PF_MEMALLOC_NOFS); >> error = xfs_log_reserve(mp, 600, 1, &tic, XFS_LOG, 0); >> + current_restore_flags_nested(&pflags, PF_MEMALLOC_NOFS); >> + >> if (error) >> goto out_err; > The more I look at this, the more I think Darrick is right and I > somewhat misinterpretted what he meant by "the top of the freeze > path". > > i.e. setting PF_MEMALLOC_NOFS here is out of place - only one caller > of xlog_unmount_write requires PF_MEMALLOC_NOFS > context. That context should be set in the caller that requires this > context, and in this case it is xfs_fs_freeze(). This is top of the > final freeze state processing (what I think Darrick meant), not the > top of the freeze syscall call chain (what I thought he meant). > > So if set PF_MEMALLOC_NOFS setting in xfs_fs_freeze(), it covers all > the allocations in this problematic path, and it should obliviates > the need for the first patch in the series altogether. > OK, I will try that and run my test. If it pass, I will post a new patch with the suggested change.
Thanks, Longman
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