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mm/gup: fix fixup_user_fault() on multiple retries 

This part was overlooked when reworking the gup code on multiple
retries.

When we get the 2nd+ retry, we'll be with TRIED flag set.  Current code
will bail out on the 2nd retry because the !TRIED check will fail so the
retry logic will be skipped.  What's worse is that, it will also return
zero which errornously hints the caller that the page is faulted in
while it's not.

The !TRIED flag check seems to not be needed even before the mutliple
retries change because if we get a VM_FAULT_RETRY, it must be the 1st
retry, and we should not have TRIED set for that.

Fix it by removing the !TRIED check, at the meantime check against fatal
signals properly before the page fault so we can still properly respond
to the user killing the process during retries.

Fixes: 4426e945df ("mm/gup: allow VM_FAULT_RETRY for multiple times")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Brian Geffon <bgeffon@google.com>
Link: http://lkml.kernel.org/r/20200502003523.8204-1-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Xu 2020-05-13 17:50:41 -07:00 committed by Linus Torvalds
parent 65759097d8
commit 475f4dfc02
1 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
mm/gup.c
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@ -1218,6 +1218,10 @@ retry:
if (!vma_permits_fault(vma, fault_flags))
return -EFAULT;
if ((fault_flags & FAULT_FLAG_KILLABLE) &&
fatal_signal_pending(current))
return -EINTR;
ret = handle_mm_fault(vma, address, fault_flags);
major |= ret & VM_FAULT_MAJOR;
if (ret & VM_FAULT_ERROR) {
@ -1230,11 +1234,9 @@ retry:
if (ret & VM_FAULT_RETRY) {
down_read(&mm->mmap_sem);
if (!(fault_flags & FAULT_FLAG_TRIED)) {
*unlocked = true;
fault_flags |= FAULT_FLAG_TRIED;
goto retry;
}
*unlocked = true;
fault_flags |= FAULT_FLAG_TRIED;
goto retry;
}
if (tsk) {