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ANDROID: userfaultfd: abort uffdio ops if mmap_lock is contended

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Check if the mmap_lock is contended when looping over the pages that
are requested to be filled. When it is observed, we rely on the already
existing mechanism to return bytes copied/filled and -EAGAIN as error.

This helps by avoiding contention of mmap_lock for long running
userfaultfd operations. The userspace can perform other tasks before
retrying the operation for the remaining pages.

Bug: 320478828
Change-Id: I6d485fd03c96a826956ee3962e58058be3cf81c1
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
This commit is contained in:
Lokesh Gidra 2024-03-08 10:59:56 -08:00
parent e3aabbf867
commit a0b6273ec3
1 changed files with 12 additions and 0 deletions
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12
mm/userfaultfd.c
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@ -664,6 +664,15 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
if (unlikely(err == -ENOENT)) {
void *page_kaddr;
/*
* Return early due to mmap_lock contention only after
* some pages are copied to ensure that jank sensitive
* threads don't keep retrying for progress-critical
* pages.
*/
if (copied && mmap_lock_is_contended(dst_mm))
break;
mmap_read_unlock(dst_mm);
BUG_ON(!page);
@ -688,6 +697,9 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
if (fatal_signal_pending(current))
err = -EINTR;
if (mmap_lock_is_contended(dst_mm))
err = -EAGAIN;
}
if (err)
break;