LU-13182 llite: Avoid eternel retry loops with MAP_POPULATE

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)

Lustre-change: https://review.whamcloud.com/40221
Lustre-commit: bb50c62c6f4cdd7a31145ab81e7c166e0760ed11

Test-Parameters: trivial testlist=sanity-hsm env=ONLY=1 clientdistro=ubuntu2004

Change-Id: I320ab9ca447282aea15ef2030ef8671c4260d895
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/43958
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>

diff --git a/lustre/llite/llite_mmap.c b/lustre/llite/llite_mmap.c
index 897c423..fee9006 100644 (file)
--- a/lustre/llite/llite_mmap.c
+++ b/lustre/llite/llite_mmap.c
@@ -279,16 +279,22 @@ static vm_fault_t ll_fault0(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 = ll_filemap_fault(vma, 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))
                        GOTO(out, result = 0);