From 698ab77aebffe08b312fbcdddeb0e8bd08b78717 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 28 Apr 2021 15:03:12 -0400 Subject: dax: Add an enum for specifying dax wakup mode Dan mentioned that he is not very fond of passing around a boolean true/false to specify if only next waiter should be woken up or all waiters should be woken up. He instead prefers that we introduce an enum and make it very explicity at the callsite itself. Easier to read code. This patch should not introduce any change of behavior. Reviewed-by: Greg Kurz Reviewed-by: Jan Kara Suggested-by: Dan Williams Signed-off-by: Vivek Goyal Link: https://lore.kernel.org/r/20210428190314.1865312-2-vgoyal@redhat.com Signed-off-by: Dan Williams --- fs/dax.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index b3d27fdc6775..5ecee51c44ee 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -144,6 +144,16 @@ struct wait_exceptional_entry_queue { struct exceptional_entry_key key; }; +/** + * enum dax_wake_mode: waitqueue wakeup behaviour + * @WAKE_ALL: wake all waiters in the waitqueue + * @WAKE_NEXT: wake only the first waiter in the waitqueue + */ +enum dax_wake_mode { + WAKE_ALL, + WAKE_NEXT, +}; + static wait_queue_head_t *dax_entry_waitqueue(struct xa_state *xas, void *entry, struct exceptional_entry_key *key) { @@ -182,7 +192,8 @@ static int wake_exceptional_entry_func(wait_queue_entry_t *wait, * The important information it's conveying is whether the entry at * this index used to be a PMD entry. */ -static void dax_wake_entry(struct xa_state *xas, void *entry, bool wake_all) +static void dax_wake_entry(struct xa_state *xas, void *entry, + enum dax_wake_mode mode) { struct exceptional_entry_key key; wait_queue_head_t *wq; @@ -196,7 +207,7 @@ static void dax_wake_entry(struct xa_state *xas, void *entry, bool wake_all) * must be in the waitqueue and the following check will see them. */ if (waitqueue_active(wq)) - __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key); + __wake_up(wq, TASK_NORMAL, mode == WAKE_ALL ? 0 : 1, &key); } /* @@ -268,7 +279,7 @@ static void put_unlocked_entry(struct xa_state *xas, void *entry) { /* If we were the only waiter woken, wake the next one */ if (entry && !dax_is_conflict(entry)) - dax_wake_entry(xas, entry, false); + dax_wake_entry(xas, entry, WAKE_NEXT); } /* @@ -286,7 +297,7 @@ static void dax_unlock_entry(struct xa_state *xas, void *entry) old = xas_store(xas, entry); xas_unlock_irq(xas); BUG_ON(!dax_is_locked(old)); - dax_wake_entry(xas, entry, false); + dax_wake_entry(xas, entry, WAKE_NEXT); } /* @@ -524,7 +535,7 @@ retry: dax_disassociate_entry(entry, mapping, false); xas_store(xas, NULL); /* undo the PMD join */ - dax_wake_entry(xas, entry, true); + dax_wake_entry(xas, entry, WAKE_ALL); mapping->nrexceptional--; entry = NULL; xas_set(xas, index); @@ -937,7 +948,7 @@ static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev, xas_lock_irq(xas); xas_store(xas, entry); xas_clear_mark(xas, PAGECACHE_TAG_DIRTY); - dax_wake_entry(xas, entry, false); + dax_wake_entry(xas, entry, WAKE_NEXT); trace_dax_writeback_one(mapping->host, index, count); return ret; -- cgit v1.2.3 From 4c3d043d271d4d629aa2328796cdfc96b37d3b3c Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 28 Apr 2021 15:03:13 -0400 Subject: dax: Add a wakeup mode parameter to put_unlocked_entry() As of now put_unlocked_entry() always wakes up next waiter. In next patches we want to wake up all waiters at one callsite. Hence, add a parameter to the function. This patch does not introduce any change of behavior. Reviewed-by: Greg Kurz Reviewed-by: Jan Kara Suggested-by: Dan Williams Signed-off-by: Vivek Goyal Link: https://lore.kernel.org/r/20210428190314.1865312-3-vgoyal@redhat.com Signed-off-by: Dan Williams --- fs/dax.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 5ecee51c44ee..56eb1c759ca5 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -275,11 +275,11 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry) finish_wait(wq, &ewait.wait); } -static void put_unlocked_entry(struct xa_state *xas, void *entry) +static void put_unlocked_entry(struct xa_state *xas, void *entry, + enum dax_wake_mode mode) { - /* If we were the only waiter woken, wake the next one */ if (entry && !dax_is_conflict(entry)) - dax_wake_entry(xas, entry, WAKE_NEXT); + dax_wake_entry(xas, entry, mode); } /* @@ -633,7 +633,7 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping, entry = get_unlocked_entry(&xas, 0); if (entry) page = dax_busy_page(entry); - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, WAKE_NEXT); if (page) break; if (++scanned % XA_CHECK_SCHED) @@ -675,7 +675,7 @@ static int __dax_invalidate_entry(struct address_space *mapping, mapping->nrexceptional--; ret = 1; out: - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, WAKE_NEXT); xas_unlock_irq(&xas); return ret; } @@ -954,7 +954,7 @@ static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev, return ret; put_unlocked: - put_unlocked_entry(xas, entry); + put_unlocked_entry(xas, entry, WAKE_NEXT); return ret; } @@ -1695,7 +1695,7 @@ dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order) /* Did we race with someone splitting entry or so? */ if (!entry || dax_is_conflict(entry) || (order == 0 && !dax_is_pte_entry(entry))) { - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, WAKE_NEXT); xas_unlock_irq(&xas); trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf, VM_FAULT_NOPAGE); -- cgit v1.2.3 From 237388320deffde7c2d65ed8fc9eef670dc979b3 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 28 Apr 2021 15:03:14 -0400 Subject: dax: Wake up all waiters after invalidating dax entry I am seeing missed wakeups which ultimately lead to a deadlock when I am using virtiofs with DAX enabled and running "make -j". I had to mount virtiofs as rootfs and also reduce to dax window size to 256M to reproduce the problem consistently. So here is the problem. put_unlocked_entry() wakes up waiters only if entry is not null as well as !dax_is_conflict(entry). But if I call multiple instances of invalidate_inode_pages2() in parallel, then I can run into a situation where there are waiters on this index but nobody will wake these waiters. invalidate_inode_pages2() invalidate_inode_pages2_range() invalidate_exceptional_entry2() dax_invalidate_mapping_entry_sync() __dax_invalidate_entry() { xas_lock_irq(&xas); entry = get_unlocked_entry(&xas, 0); ... ... dax_disassociate_entry(entry, mapping, trunc); xas_store(&xas, NULL); ... ... put_unlocked_entry(&xas, entry); xas_unlock_irq(&xas); } Say a fault in in progress and it has locked entry at offset say "0x1c". Now say three instances of invalidate_inode_pages2() are in progress (A, B, C) and they all try to invalidate entry at offset "0x1c". Given dax entry is locked, all tree instances A, B, C will wait in wait queue. When dax fault finishes, say A is woken up. It will store NULL entry at index "0x1c" and wake up B. When B comes along it will find "entry=0" at page offset 0x1c and it will call put_unlocked_entry(&xas, 0). And this means put_unlocked_entry() will not wake up next waiter, given the current code. And that means C continues to wait and is not woken up. This patch fixes the issue by waking up all waiters when a dax entry has been invalidated. This seems to fix the deadlock I am facing and I can make forward progress. Reported-by: Sergio Lopez Fixes: ac401cc78242 ("dax: New fault locking") Reviewed-by: Jan Kara Suggested-by: Dan Williams Signed-off-by: Vivek Goyal Link: https://lore.kernel.org/r/20210428190314.1865312-4-vgoyal@redhat.com Signed-off-by: Dan Williams --- fs/dax.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index 56eb1c759ca5..df5485b4bddf 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -675,7 +675,7 @@ static int __dax_invalidate_entry(struct address_space *mapping, mapping->nrexceptional--; ret = 1; out: - put_unlocked_entry(&xas, entry, WAKE_NEXT); + put_unlocked_entry(&xas, entry, WAKE_ALL); xas_unlock_irq(&xas); return ret; } -- cgit v1.2.3