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9.4.14

940014

05-12-2023

[LU-17295] avoiding VFS exclusive locking on shared parent directory in ->atomic_open() https://jira.whamcloud.com/browse/LU-17295 Lustre <p>This is an experimental feature to avoid the VFS exclusive locking on parent directory in ->atomic_open during file creations.</p> <p>It converted the exclusive semaphore mutex into a shared lock to avoid waiting for the heavy creation RPC to finished </p> LU-17295

avoiding VFS exclusive locking on shared parent directory in ->atomic_open()

Improvement Minor Open Unresolved Qian Yingjin Qian Yingjin Fri, 17 Nov 2023 03:20:41 +0000 Mon, 18 Dec 2023 23:21:22 +0000 0 5 <p>Found a possible bug in Lustre:</p> <p> </p> <div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent"> <pre class="code-java"> <span class="code-keyword">static</span> <span class="code-object">int</span> ll_atomic_open() <span class="code-comment">/* VFS has locked the inode before calling <span class="code-keyword">this</span> */</span> ll_set_inode_lock_owner(dir); </pre> </div></div> <p>As the dir maybe lock in shared mode, we may wrongly thought that the @dir is locked in exclusive mode:</p> <p> </p> <div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent"> <pre class="code-java"> <span class="code-keyword">if</span> (open_flag & O_CREAT) inode_lock(dir->d_inode); <span class="code-keyword">else</span> inode_lock_shared(dir->d_inode); error = lookup_open(nd, &path, file, op, got_write); <span class="code-keyword">if</span> (open_flag & O_CREAT) inode_unlock(dir->d_inode); <span class="code-keyword">else</span> inode_unlock_shared(dir->d_inode); </pre> </div></div> <p> </p> <p>in vvp_inode_ops(),</p> <p>we may unlock the inode wrongly...</p> <p> </p> <div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent"> <pre class="code-java"> <span class="code-keyword">case</span> COIO_INODE_UNLOCK: <span class="code-keyword">if</span> (ll_get_inode_lock_owner(inode) == current) ll_inode_unlock(inode); </pre> </div></div> <p> </p> <p> </p> <p> </p> <p>"Qian Yingjin <qian@ddn.com>" uploaded a new patch: <a href="https://review.whamcloud.com/c/fs/lustre-release/+/53169" class="external-link" target="_blank" rel="nofollow noopener">https://review.whamcloud.com/c/fs/lustre-release/+/53169</a><br/> Subject: <a href="https://jira.whamcloud.com/browse/LU-17295" title="avoiding VFS exclusive locking on shared parent directory in ->atomic_open()" class="issue-link" data-issue-key="LU-17295">LU-17295</a> llite: avoid VFS exclusive locking in atomic_open<br/> Project: fs/lustre-release<br/> Branch: master<br/> Current Patch Set: 1<br/> Commit: a5d02885d5eaacaefc10c7962056587b74199daf</p> Related Development Rank 1|i0423b: Rank (Obsolete) 9223372036854775807 Severity