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authorLinus Torvalds <torvalds@linux-foundation.org>2019-03-15 19:00:45 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2019-03-15 19:00:45 (GMT)
commitf91f2ee54a21404fbc633550e99d69d14c2478f2 (patch)
tree19620c0e3098d97567c119162a6111e4f7b7a5cc
parentf261c4e529dac5608a604d3dd3ae1cd2adf23c89 (diff)
parent8b0f9fa2e02dc95216577c3387b0707c5f60fbaf (diff)
Merge branch 'akpm' (rest of patches from Andrew)
Merge the left-over patches from Andrew Morton. This merges the remaining two patches from Andrew's pile of "little bit more MM". I mulled it over, and we emailed back and forth with Josef, and he pointed out where I was wrong. Rule #51 of kernel maintenance: when somebody makes it clear that they know the code better than you did, stop arguing and just apply the damn patch. Add a third patch by me to add a comment for the case that I had thought was buggy and Josef corrected me on. * emailed patches from Andrew Morton <akpm@linux-foundation.org>: filemap: add a comment about FAULT_FLAG_RETRY_NOWAIT behavior filemap: drop the mmap_sem for all blocking operations filemap: kill page_cache_read usage in filemap_fault
-rw-r--r--include/linux/pagemap.h1
-rw-r--r--mm/filemap.c202
2 files changed, 131 insertions, 72 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index b477a70..bcf909d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -239,6 +239,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_WRITE 0x00000008
#define FGP_NOFS 0x00000010
#define FGP_NOWAIT 0x00000020
+#define FGP_FOR_MMAP 0x00000040
struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
int fgp_flags, gfp_t cache_gfp_mask);
diff --git a/mm/filemap.c b/mm/filemap.c
index ec6566ff..d78f577 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1587,6 +1587,9 @@ EXPORT_SYMBOL(find_lock_entry);
* @gfp_mask and added to the page cache and the VM's LRU
* list. The page is returned locked and with an increased
* refcount.
+ * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do
+ * its own locking dance if the page is already in cache, or unlock the page
+ * before returning if we had to add the page to pagecache.
*
* If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
* if the GFP flags specified for FGP_CREAT are atomic.
@@ -1641,7 +1644,7 @@ no_page:
if (!page)
return NULL;
- if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
+ if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
fgp_flags |= FGP_LOCK;
/* Init accessed so avoid atomic mark_page_accessed later */
@@ -1655,6 +1658,13 @@ no_page:
if (err == -EEXIST)
goto repeat;
}
+
+ /*
+ * add_to_page_cache_lru locks the page, and for mmap we expect
+ * an unlocked page.
+ */
+ if (page && (fgp_flags & FGP_FOR_MMAP))
+ unlock_page(page);
}
return page;
@@ -2379,64 +2389,98 @@ out:
EXPORT_SYMBOL(generic_file_read_iter);
#ifdef CONFIG_MMU
-/**
- * page_cache_read - adds requested page to the page cache if not already there
- * @file: file to read
- * @offset: page index
- * @gfp_mask: memory allocation flags
- *
- * This adds the requested page to the page cache if it isn't already there,
- * and schedules an I/O to read in its contents from disk.
- *
- * Return: %0 on success, negative error code otherwise.
- */
-static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
+#define MMAP_LOTSAMISS (100)
+static struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
+ struct file *fpin)
{
- struct address_space *mapping = file->f_mapping;
- struct page *page;
- int ret;
+ int flags = vmf->flags;
- do {
- page = __page_cache_alloc(gfp_mask);
- if (!page)
- return -ENOMEM;
+ if (fpin)
+ return fpin;
- ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
- if (ret == 0)
- ret = mapping->a_ops->readpage(file, page);
- else if (ret == -EEXIST)
- ret = 0; /* losing race to add is OK */
+ /*
+ * FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
+ * anything, so we only pin the file and drop the mmap_sem if only
+ * FAULT_FLAG_ALLOW_RETRY is set.
+ */
+ if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
+ FAULT_FLAG_ALLOW_RETRY) {
+ fpin = get_file(vmf->vma->vm_file);
+ up_read(&vmf->vma->vm_mm->mmap_sem);
+ }
+ return fpin;
+}
- put_page(page);
+/*
+ * lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_sem
+ * @vmf - the vm_fault for this fault.
+ * @page - the page to lock.
+ * @fpin - the pointer to the file we may pin (or is already pinned).
+ *
+ * This works similar to lock_page_or_retry in that it can drop the mmap_sem.
+ * It differs in that it actually returns the page locked if it returns 1 and 0
+ * if it couldn't lock the page. If we did have to drop the mmap_sem then fpin
+ * will point to the pinned file and needs to be fput()'ed at a later point.
+ */
+static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
+ struct file **fpin)
+{
+ if (trylock_page(page))
+ return 1;
- } while (ret == AOP_TRUNCATED_PAGE);
+ /*
+ * NOTE! This will make us return with VM_FAULT_RETRY, but with
+ * the mmap_sem still held. That's how FAULT_FLAG_RETRY_NOWAIT
+ * is supposed to work. We have way too many special cases..
+ */
+ if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+ return 0;
- return ret;
+ *fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
+ if (vmf->flags & FAULT_FLAG_KILLABLE) {
+ if (__lock_page_killable(page)) {
+ /*
+ * We didn't have the right flags to drop the mmap_sem,
+ * but all fault_handlers only check for fatal signals
+ * if we return VM_FAULT_RETRY, so we need to drop the
+ * mmap_sem here and return 0 if we don't have a fpin.
+ */
+ if (*fpin == NULL)
+ up_read(&vmf->vma->vm_mm->mmap_sem);
+ return 0;
+ }
+ } else
+ __lock_page(page);
+ return 1;
}
-#define MMAP_LOTSAMISS (100)
/*
- * Synchronous readahead happens when we don't even find
- * a page in the page cache at all.
+ * Synchronous readahead happens when we don't even find a page in the page
+ * cache at all. We don't want to perform IO under the mmap sem, so if we have
+ * to drop the mmap sem we return the file that was pinned in order for us to do
+ * that. If we didn't pin a file then we return NULL. The file that is
+ * returned needs to be fput()'ed when we're done with it.
*/
-static void do_sync_mmap_readahead(struct vm_fault *vmf)
+static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
{
struct file *file = vmf->vma->vm_file;
struct file_ra_state *ra = &file->f_ra;
struct address_space *mapping = file->f_mapping;
+ struct file *fpin = NULL;
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ)
- return;
+ return fpin;
if (!ra->ra_pages)
- return;
+ return fpin;
if (vmf->vma->vm_flags & VM_SEQ_READ) {
+ fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_sync_readahead(mapping, ra, file, offset,
ra->ra_pages);
- return;
+ return fpin;
}
/* Avoid banging the cache line if not needed */
@@ -2448,37 +2492,44 @@ static void do_sync_mmap_readahead(struct vm_fault *vmf)
* stop bothering with read-ahead. It will only hurt.
*/
if (ra->mmap_miss > MMAP_LOTSAMISS)
- return;
+ return fpin;
/*
* mmap read-around
*/
+ fpin = maybe_unlock_mmap_for_io(vmf, fpin);
ra->start = max_t(long, 0, offset - ra->ra_pages / 2);
ra->size = ra->ra_pages;
ra->async_size = ra->ra_pages / 4;
ra_submit(ra, mapping, file);
+ return fpin;
}
/*
* Asynchronous readahead happens when we find the page and PG_readahead,
- * so we want to possibly extend the readahead further..
+ * so we want to possibly extend the readahead further. We return the file that
+ * was pinned if we have to drop the mmap_sem in order to do IO.
*/
-static void do_async_mmap_readahead(struct vm_fault *vmf,
- struct page *page)
+static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
+ struct page *page)
{
struct file *file = vmf->vma->vm_file;
struct file_ra_state *ra = &file->f_ra;
struct address_space *mapping = file->f_mapping;
+ struct file *fpin = NULL;
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ)
- return;
+ return fpin;
if (ra->mmap_miss > 0)
ra->mmap_miss--;
- if (PageReadahead(page))
+ if (PageReadahead(page)) {
+ fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_async_readahead(mapping, ra, file,
page, offset, ra->ra_pages);
+ }
+ return fpin;
}
/**
@@ -2510,6 +2561,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
{
int error;
struct file *file = vmf->vma->vm_file;
+ struct file *fpin = NULL;
struct address_space *mapping = file->f_mapping;
struct file_ra_state *ra = &file->f_ra;
struct inode *inode = mapping->host;
@@ -2531,23 +2583,26 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
* We found the page, so try async readahead before
* waiting for the lock.
*/
- do_async_mmap_readahead(vmf, page);
+ fpin = do_async_mmap_readahead(vmf, page);
} else if (!page) {
/* No page in the page cache at all */
- do_sync_mmap_readahead(vmf);
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
ret = VM_FAULT_MAJOR;
+ fpin = do_sync_mmap_readahead(vmf);
retry_find:
- page = find_get_page(mapping, offset);
- if (!page)
- goto no_cached_page;
+ page = pagecache_get_page(mapping, offset,
+ FGP_CREAT|FGP_FOR_MMAP,
+ vmf->gfp_mask);
+ if (!page) {
+ if (fpin)
+ goto out_retry;
+ return vmf_error(-ENOMEM);
+ }
}
- if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
- put_page(page);
- return ret | VM_FAULT_RETRY;
- }
+ if (!lock_page_maybe_drop_mmap(vmf, page, &fpin))
+ goto out_retry;
/* Did it get truncated? */
if (unlikely(page->mapping != mapping)) {
@@ -2565,6 +2620,16 @@ retry_find:
goto page_not_uptodate;
/*
+ * We've made it this far and we had to drop our mmap_sem, now is the
+ * time to return to the upper layer and have it re-find the vma and
+ * redo the fault.
+ */
+ if (fpin) {
+ unlock_page(page);
+ goto out_retry;
+ }
+
+ /*
* Found the page and have a reference on it.
* We must recheck i_size under page lock.
*/
@@ -2578,28 +2643,6 @@ retry_find:
vmf->page = page;
return ret | VM_FAULT_LOCKED;
-no_cached_page:
- /*
- * We're only likely to ever get here if MADV_RANDOM is in
- * effect.
- */
- error = page_cache_read(file, offset, vmf->gfp_mask);
-
- /*
- * The page we want has now been added to the page cache.
- * In the unlikely event that someone removed it in the
- * meantime, we'll just come back here and read it again.
- */
- if (error >= 0)
- goto retry_find;
-
- /*
- * An error return from page_cache_read can result if the
- * system is low on memory, or a problem occurs while trying
- * to schedule I/O.
- */
- return vmf_error(error);
-
page_not_uptodate:
/*
* Umm, take care of errors if the page isn't up-to-date.
@@ -2608,12 +2651,15 @@ page_not_uptodate:
* and we need to check for errors.
*/
ClearPageError(page);
+ fpin = maybe_unlock_mmap_for_io(vmf, fpin);
error = mapping->a_ops->readpage(file, page);
if (!error) {
wait_on_page_locked(page);
if (!PageUptodate(page))
error = -EIO;
}
+ if (fpin)
+ goto out_retry;
put_page(page);
if (!error || error == AOP_TRUNCATED_PAGE)
@@ -2622,6 +2668,18 @@ page_not_uptodate:
/* Things didn't work out. Return zero to tell the mm layer so. */
shrink_readahead_size_eio(file, ra);
return VM_FAULT_SIGBUS;
+
+out_retry:
+ /*
+ * We dropped the mmap_sem, we need to return to the fault handler to
+ * re-find the vma and come back and find our hopefully still populated
+ * page.
+ */
+ if (page)
+ put_page(page);
+ if (fpin)
+ fput(fpin);
+ return ret | VM_FAULT_RETRY;
}
EXPORT_SYMBOL(filemap_fault);

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