[lustre-devel] [PATCH 21/28] lustre: llite: Avoid eternel retry loops with MAP_POPULATE
James Simmons
jsimmons at infradead.org
Sun Nov 15 16:59:54 PST 2020
From: Oleg Drokin <green at whamcloud.com>
Kernels 5.4+ have an infinite retry loop from MAP_POPULATE mmap
option. Use the FAULT_FLAG_RETRY_NOWAIT to instruct filemap_fault
to not drop the mmap_sem so if the call fails, we could use
the slow path and break the loop from forming.
(Idea by Neil Brown)
WC-bug-id: https://jira.whamcloud.com/browse/LU-13182
Lustre-commit: bb50c62c6f4cdd ("LU-13182 llite: Avoid eternel retry loops with MAP_POPULATE")
Signed-off-by: Oleg Drokin <green at whamcloud.com>
Reviewed-on: https://review.whamcloud.com/40221
Reviewed-by: Neil Brown <neilb at suse.de>
Reviewed-by: James Simmons <jsimmons at infradead.org>
Signed-off-by: James Simmons <jsimmons at infradead.org>
---
fs/lustre/llite/llite_mmap.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/fs/lustre/llite/llite_mmap.c b/fs/lustre/llite/llite_mmap.c
index f77b8f9..f0be7ba 100644
--- a/fs/lustre/llite/llite_mmap.c
+++ b/fs/lustre/llite/llite_mmap.c
@@ -288,18 +288,24 @@ static vm_fault_t __ll_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
if (ll_sbi_has_fast_read(ll_i2sbi(file_inode(vma->vm_file)))) {
/* do fast fault */
+ 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;
ll_cl_add(vma->vm_file, env, NULL, LCC_MMAP);
fault_ret = filemap_fault(vmf);
ll_cl_remove(vma->vm_file, env);
+ if (has_retry)
+ vmf->flags &= ~FAULT_FLAG_RETRY_NOWAIT;
/*
* - If there is no error, then the page was found in cache and
* uptodate;
* - If VM_FAULT_RETRY is set, the page existed but failed to
- * lock. It will return to kernel and retry;
+ * lock. We will try slow path to avoid loops.
* - Otherwise, it should try normal fault under DLM lock.
*/
- if ((fault_ret & VM_FAULT_RETRY) ||
+ if (!(fault_ret & VM_FAULT_RETRY) &&
!(fault_ret & VM_FAULT_ERROR)) {
result = 0;
goto out;
--
1.8.3.1
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