Commit 2aa6ba7b authored by Darrick J. Wong's avatar Darrick J. Wong

xfs: clear _XBF_PAGES from buffers when readahead page

If we try to allocate memory pages to back an xfs_buf that we're trying
to read, it's possible that we'll be so short on memory that the page
allocation fails.  For a blocking read we'll just wait, but for
readahead we simply dump all the pages we've collected so far.

Unfortunately, after dumping the pages we neglect to clear the
_XBF_PAGES state, which means that the subsequent call to xfs_buf_free
thinks that b_pages still points to pages we own.  It then double-frees
the b_pages pages.

This results in screaming about negative page refcounts from the memory
manager, which xfs oughtn't be triggering.  To reproduce this case,
mount a filesystem where the size of the inodes far outweighs the
availalble memory (a ~500M inode filesystem on a VM with 300MB memory
did the trick here) and run bulkstat in parallel with other memory
eating processes to put a huge load on the system.  The "check summary"
phase of xfs_scrub also works for this purpose.
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: default avatarEric Sandeen <sandeen@redhat.com>
parent 493611eb
...@@ -422,6 +422,7 @@ xfs_buf_allocate_memory( ...@@ -422,6 +422,7 @@ xfs_buf_allocate_memory(
out_free_pages: out_free_pages:
for (i = 0; i < bp->b_page_count; i++) for (i = 0; i < bp->b_page_count; i++)
__free_page(bp->b_pages[i]); __free_page(bp->b_pages[i]);
bp->b_flags &= ~_XBF_PAGES;
return error; return error;
} }
......
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