diff options
| author | Gao Xiang <hsiangkao@redhat.com> | 2020-09-23 09:26:31 -0700 |
|---|---|---|
| committer | Darrick J. Wong <darrick.wong@oracle.com> | 2020-09-25 11:34:08 -0700 |
| commit | b38e07401ec7e6eefc1f84e682f5b75ce3a685e5 (patch) | |
| tree | 446ac2c3a9e7cbac72a524c7df3816b649a5cdba /fs/xfs | |
| parent | 61ef5230518a3ad224549a50a01b73989acb94b9 (diff) | |
xfs: drop the obsolete comment on filestream locking
Since commit 1c1c6ebcf52 ("xfs: Replace per-ag array with a radix
tree"), there is no m_peraglock anymore, so it's hard to understand
the described situation since per-ag is no longer an array and no
need to reallocate, call xfs_filestream_flush() in growfs.
In addition, the race condition for shrink feature is quite confusing
to me currently as well. Get rid of it instead.
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'fs/xfs')
| -rw-r--r-- | fs/xfs/xfs_filestream.c | 34 |
1 files changed, 1 insertions, 33 deletions
diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c index 1a88025e68a3..db23e455eb91 100644 --- a/fs/xfs/xfs_filestream.c +++ b/fs/xfs/xfs_filestream.c @@ -33,39 +33,7 @@ enum xfs_fstrm_alloc { /* * Allocation group filestream associations are tracked with per-ag atomic * counters. These counters allow xfs_filestream_pick_ag() to tell whether a - * particular AG already has active filestreams associated with it. The mount - * point's m_peraglock is used to protect these counters from per-ag array - * re-allocation during a growfs operation. When xfs_growfs_data_private() is - * about to reallocate the array, it calls xfs_filestream_flush() with the - * m_peraglock held in write mode. - * - * Since xfs_mru_cache_flush() guarantees that all the free functions for all - * the cache elements have finished executing before it returns, it's safe for - * the free functions to use the atomic counters without m_peraglock protection. - * This allows the implementation of xfs_fstrm_free_func() to be agnostic about - * whether it was called with the m_peraglock held in read mode, write mode or - * not held at all. The race condition this addresses is the following: - * - * - The work queue scheduler fires and pulls a filestream directory cache - * element off the LRU end of the cache for deletion, then gets pre-empted. - * - A growfs operation grabs the m_peraglock in write mode, flushes all the - * remaining items from the cache and reallocates the mount point's per-ag - * array, resetting all the counters to zero. - * - The work queue thread resumes and calls the free function for the element - * it started cleaning up earlier. In the process it decrements the - * filestreams counter for an AG that now has no references. - * - * With a shrinkfs feature, the above scenario could panic the system. - * - * All other uses of the following macros should be protected by either the - * m_peraglock held in read mode, or the cache's internal locking exposed by the - * interval between a call to xfs_mru_cache_lookup() and a call to - * xfs_mru_cache_done(). In addition, the m_peraglock must be held in read mode - * when new elements are added to the cache. - * - * Combined, these locking rules ensure that no associations will ever exist in - * the cache that reference per-ag array elements that have since been - * reallocated. + * particular AG already has active filestreams associated with it. */ int xfs_filestream_peek_ag( |