File 0042-LU-14713-llite-tighten-condition-for-fault... of Package lustre_2_12

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File 0042-LU-14713-llite-tighten-condition-for-fault-not-drop-.patch of Package lustre_2_12

From 81aec05103558f57adb10fd319847304cdf44aa7 Mon Sep 17 00:00:00 2001
From: Bobi Jam <bobijam@whamcloud.com>
Date: Fri, 3 Sep 2021 00:38:43 +0800
Subject: [PATCH] LU-14713 llite: tighten condition for fault not drop mmap_sem

As __lock_page_or_retry() indicates, filemap_fault() will return
VM_FAULT_RETRY without releasing mmap_sem iff flags contains
FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT.

So ll_fault0() should pass in FAULT_FLAG_ALLOW_RETRY |
FAULT_FLAG_RETRY_NOWAIT in ll_filemap_fault() so that when it
returns VM_FAULT_RETRY, we can pass on trying normal fault
under DLM lock as mmap_sem is still being held.

While in Linux 5.1 (6b4c9f4469819) FAULT_FLAG_RETRY_NOWAIT is enough
to not drop mmap_sem when failed to lock the page.

Fixes: 87865e4ae9 ("LU-13182 llite: Avoid eternel retry loops with MAP_POPULATE")
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I9420c587301722b597155558657577349a8141e4
Reviewed-on: https://review.whamcloud.com/44715
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
---
 lustre/llite/llite_mmap.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/lustre/llite/llite_mmap.c
+++ b/lustre/llite/llite_mmap.c
@@ -280,15 +280,23 @@ static vm_fault_t ll_fault0(struct vm_ar
 
 	if (ll_sbi_has_fast_read(ll_i2sbi(file_inode(vma->vm_file)))) {
 		/* do fast fault */
+		bool allow_retry = vmf->flags & FAULT_FLAG_ALLOW_RETRY;
 		bool has_retry = vmf->flags & FAULT_FLAG_RETRY_NOWAIT;
 
 		/* To avoid loops, instruct downstream to not drop mmap_sem */
-		vmf->flags |= FAULT_FLAG_RETRY_NOWAIT;
+		/**
+		 * only need FAULT_FLAG_ALLOW_RETRY prior to Linux 5.1
+		 * (6b4c9f4469819), where FAULT_FLAG_RETRY_NOWAIT is enough
+		 * to not drop mmap_sem when failed to lock the page.
+		 */
+		vmf->flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 		ll_cl_add(vma->vm_file, env, NULL, LCC_MMAP);
 		fault_ret = ll_filemap_fault(vma, vmf);
 		ll_cl_remove(vma->vm_file, env);
 		if (!has_retry)
 			vmf->flags &= ~FAULT_FLAG_RETRY_NOWAIT;
+		if (!allow_retry)
+			vmf->flags &= ~FAULT_FLAG_ALLOW_RETRY;
 
 		/* - If there is no error, then the page was found in cache and
 		 *   uptodate;

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File 0042-LU-14713-llite-tighten-condition-for-fault-not-drop-.patch of Package lustre_2_12

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