Re: [PATCH v1 7/7] fs/proc/kcore: use page_offline_(freeze|unfreeze)
From: Mike Rapoport <rppt@kernel.org>
Date: 2021-05-02 06:34:24
Also in:
linux-fsdevel, linux-mm, lkml
On Thu, Apr 29, 2021 at 02:25:19PM +0200, David Hildenbrand wrote:
quoted hunk ↗ jump to hunk
Let's properly synchronize with drivers that set PageOffline(). Unfreeze every now and then, so drivers that want to set PageOffline() can make progress. Signed-off-by: David Hildenbrand <redacted> --- fs/proc/kcore.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c index 92ff1e4436cb..3d7531f47389 100644 --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c@@ -311,6 +311,7 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, static ssize_t read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) { + size_t page_offline_frozen = 0; char *buf = file->private_data; size_t phdrs_offset, notes_offset, data_offset; size_t phdrs_len, notes_len;@@ -509,6 +510,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) pfn = __pa(start) >> PAGE_SHIFT; page = pfn_to_online_page(pfn);
Can't this race with page offlining for the first time we get here?
+ /*
+ * Don't race against drivers that set PageOffline()
+ * and expect no further page access.
+ */
+ if (page_offline_frozen == MAX_ORDER_NR_PAGES) {
+ page_offline_unfreeze();
+ page_offline_frozen = 0;
+ cond_resched();
+ }
+ if (!page_offline_frozen++)
+ page_offline_freeze();
+Don't we need to freeze before doing pfn_to_online_page()?
quoted hunk ↗ jump to hunk
/* * Don't read offline sections, logically offline pages * (e.g., inflated in a balloon), hwpoisoned pages,@@ -565,6 +578,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) } out: + if (page_offline_frozen) + page_offline_unfreeze(); up_read(&kclist_lock); if (ret) return ret;-- 2.30.2
-- Sincerely yours, Mike.