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shmem: factor shmem_falloc_wait() out of shmem_fault() 

That Trinity livelock shmem_falloc avoidance block is unlikely, and a
distraction from the proper business of shmem_fault(): separate it out. 
(This used to help compilers save stack on the fault path too, but both
gcc and clang nowadays seem to make better choices anyway.)

Link: https://lkml.kernel.org/r/6fe379a4-6176-9225-9263-fe60d2633c0@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2023-09-29 20:27:53 -07:00 committed by Andrew Morton
parent e3e1a5067f
commit f0a9ad1d4d
1 changed files with 69 additions and 57 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

126
mm/shmem.c
View File

@ -2148,87 +2148,99 @@ int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
* entry unconditionally - even if something else had already woken the
* target.
*/
static int synchronous_wake_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
static int synchronous_wake_function(wait_queue_entry_t *wait,
unsigned int mode, int sync, void *key)
{
int ret = default_wake_function(wait, mode, sync, key);
list_del_init(&wait->entry);
return ret;
}
/*
* Trinity finds that probing a hole which tmpfs is punching can
* prevent the hole-punch from ever completing: which in turn
* locks writers out with its hold on i_rwsem. So refrain from
* faulting pages into the hole while it's being punched. Although
* shmem_undo_range() does remove the additions, it may be unable to
* keep up, as each new page needs its own unmap_mapping_range() call,
* and the i_mmap tree grows ever slower to scan if new vmas are added.
*
* It does not matter if we sometimes reach this check just before the
* hole-punch begins, so that one fault then races with the punch:
* we just need to make racing faults a rare case.
*
* The implementation below would be much simpler if we just used a
* standard mutex or completion: but we cannot take i_rwsem in fault,
* and bloating every shmem inode for this unlikely case would be sad.
*/
static vm_fault_t shmem_falloc_wait(struct vm_fault *vmf, struct inode *inode)
{
struct shmem_falloc *shmem_falloc;
struct file *fpin = NULL;
vm_fault_t ret = 0;
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
if (shmem_falloc &&
shmem_falloc->waitq &&
vmf->pgoff >= shmem_falloc->start &&
vmf->pgoff < shmem_falloc->next) {
wait_queue_head_t *shmem_falloc_waitq;
DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);
ret = VM_FAULT_NOPAGE;
fpin = maybe_unlock_mmap_for_io(vmf, NULL);
shmem_falloc_waitq = shmem_falloc->waitq;
prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
TASK_UNINTERRUPTIBLE);
spin_unlock(&inode->i_lock);
schedule();
/*
* shmem_falloc_waitq points into the shmem_fallocate()
* stack of the hole-punching task: shmem_falloc_waitq
* is usually invalid by the time we reach here, but
* finish_wait() does not dereference it in that case;
* though i_lock needed lest racing with wake_up_all().
*/
spin_lock(&inode->i_lock);
finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
}
spin_unlock(&inode->i_lock);
if (fpin) {
fput(fpin);
ret = VM_FAULT_RETRY;
}
return ret;
}
static vm_fault_t shmem_fault(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct inode *inode = file_inode(vma->vm_file);
struct inode *inode = file_inode(vmf->vma->vm_file);
gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
struct folio *folio = NULL;
vm_fault_t ret = 0;
int err;
vm_fault_t ret = VM_FAULT_LOCKED;
/*
* Trinity finds that probing a hole which tmpfs is punching can
* prevent the hole-punch from ever completing: which in turn
* locks writers out with its hold on i_rwsem. So refrain from
* faulting pages into the hole while it's being punched. Although
* shmem_undo_range() does remove the additions, it may be unable to
* keep up, as each new page needs its own unmap_mapping_range() call,
* and the i_mmap tree grows ever slower to scan if new vmas are added.
*
* It does not matter if we sometimes reach this check just before the
* hole-punch begins, so that one fault then races with the punch:
* we just need to make racing faults a rare case.
*
* The implementation below would be much simpler if we just used a
* standard mutex or completion: but we cannot take i_rwsem in fault,
* and bloating every shmem inode for this unlikely case would be sad.
* prevent the hole-punch from ever completing: noted in i_private.
*/
if (unlikely(inode->i_private)) {
struct shmem_falloc *shmem_falloc;
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
if (shmem_falloc &&
shmem_falloc->waitq &&
vmf->pgoff >= shmem_falloc->start &&
vmf->pgoff < shmem_falloc->next) {
struct file *fpin;
wait_queue_head_t *shmem_falloc_waitq;
DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);
ret = VM_FAULT_NOPAGE;
fpin = maybe_unlock_mmap_for_io(vmf, NULL);
if (fpin)
ret = VM_FAULT_RETRY;
shmem_falloc_waitq = shmem_falloc->waitq;
prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
TASK_UNINTERRUPTIBLE);
spin_unlock(&inode->i_lock);
schedule();
/*
* shmem_falloc_waitq points into the shmem_fallocate()
* stack of the hole-punching task: shmem_falloc_waitq
* is usually invalid by the time we reach here, but
* finish_wait() does not dereference it in that case;
* though i_lock needed lest racing with wake_up_all().
*/
spin_lock(&inode->i_lock);
finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
spin_unlock(&inode->i_lock);
if (fpin)
fput(fpin);
ret = shmem_falloc_wait(vmf, inode);
if (ret)
return ret;
}
spin_unlock(&inode->i_lock);
}
WARN_ON_ONCE(vmf->page != NULL);
err = shmem_get_folio_gfp(inode, vmf->pgoff, &folio, SGP_CACHE,
gfp, vmf, &ret);
if (err)
return vmf_error(err);
if (folio)
if (folio) {
vmf->page = folio_file_page(folio, vmf->pgoff);
ret |= VM_FAULT_LOCKED;
}
return ret;
}