Details
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Improvement
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Resolution: Fixed
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Minor
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None
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None
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9223372036854775807
Description
The inode->i_mutex should be held when calling osd_execute_truncate->ldiskfs_truncate(). However, due to locking order in osd-ldiskfs we cannot just grab i_mutex around ldiskfs_truncate() as that can lead to deadlocks as described in LU-6446 and LU-4252.
Currently, there is an ldiskfs patch to remove the WARN_ON() in ext4_truncate() when it is called without i_mutex held. This is safe because the osd-ldiskfs code holds its own lock (oo_ext_idx_sem) on the object over the ldiskfs_truncate() call, but potentially there is a way to improve this without patching the ldiskfs code.
The truncate-warning patch was first added with:
commit 3daba43a191a0a2c9358d39b3f48b1b759a41819 Author: Yang Sheng <yang.sheng@intel.com> LU-6446 ldiskfs: remove WARN_ON from ldiskfs_orphan_add{del} RHEL7.1 kernel carefully check i_mutex whether locked in many places. It will be triggered while ldiskfs_truncate() was invoked in osd layer. A dead lock would occured if we just locked i_mutex around it since Lustre using a reverse order for start journal==>lock i_mutex. Consider Lustre has own ldlm lock. So just remove such messages in ldiskfs patches. Reviewed-on: http://review.whamcloud.com/14690
so I think moving the lock is not as easily done as what is done in the current patch, see comments in LU-6446 and LU-4252 for details. The code used to look like the following:
if (!(inode->i_state & (I_NEW|I_FREEING))) mutex_lock(&inode->i_mutex); ldiskfs_truncate(inode); if (!(inode->i_state & (I_NEW|I_FREEING))) mutex_unlock(&inode->i_mutex);
but this was removed as part of the patch:
commit b98792ae96ad2bb3c73ca3ebebdd8edfdfbc35df Author: yangsheng <yang.sheng@intel.com> LU-4252 osd: remove locking i_mutex in osd_punch This piece of code intent to calm down the kernel WARN_ON messsage show up since 3.9 upstream. So we can just remove it for now. We'll add a ldiskfs patch to resolve this issue while 3.9 server support come up. Reviewed-on: http://review.whamcloud.com/9644
In more recent developments, LU-10048 changed the truncate code so that it is called asynchronously from the main transaction, so that it doesn't bloat transaction sizes, and avoids lock ordering issues:
commit cf29a5e7bfa254ccfcea023028fe7da80503c512 Author: Alex Zhuravlev <alexey.zhuravlev@intel.com> LU-10048 osd: async truncate osd-ldiskfs should execute truncate outside of main transaction handle. This avoids restarting truncate transaction handles in main transaction, and allows "transaction first, locking second" model on OST. Reviewed-on: https://review.whamcloud.com/27488
It may now be OK to grab i_mutex around ldiskfs_truncate() in osd_execute_truncate() and remove ext4-remove-truncate-warning.patch, but this should be reviewed and tested properly (e.g. with the racer workload that triggered LU-4252 originally).
Attachments
Issue Links
- is related to
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LU-13234 ldiskfs/namei.c:3310 ldiskfs_orphan_add+0x11e/0x2a0 [ldiskfs]
- Resolved
- is related to
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LU-4252 Failure on test suite racer test_1
- Resolved
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LU-6446 Warn-on in ldiskfs_orphan_add/del
- Resolved
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LU-10048 osd-ldiskfs to truncate outside of main transaction
- Resolved
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LU-11832 ARM servers crashing on MDS startup
- Resolved
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LU-13183 Linux 5.4 ldiskfs build (drop: ext4-remove-truncate-warning.patch)
- Resolved