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Fix NULL deref in balance_pgdat() 

Be careful not to unconditionally clear the PF_MEMALLOC bit in
the task structure.  It may have already been set when entering
zpl_putpage() in which case it must remain set on exit.  In
particular the kswapd thread will have PF_MEMALLOC set in
order to prevent it from entering direct reclaim.  By clearing
it we allow the following NULL deref to potentially occur.

  BUG: unable to handle kernel NULL pointer dereference at (null)
  IP: [<ffffffff8109c7ab>] balance_pgdat+0x25b/0x4ff

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #287
This commit is contained in:
Brian Behlendorf 2011-11-01 13:07:41 -07:00
parent a7b125e9a5
commit 6a95d0b74c
1 changed files with 7 additions and 3 deletions
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10
module/zfs/zpl_file.c
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@ -324,9 +324,13 @@ zpl_putpage(struct page *pp, struct writeback_control *wbc, void *data)
* the VM might try to write out additional pages by calling
* zpl_putpage() again resulting in a deadlock.
*/
current->flags |= PF_MEMALLOC;
(void) zfs_putpage(mapping->host, pp, wbc);
current->flags &= ~PF_MEMALLOC;
if (current->flags & PF_MEMALLOC) {
(void) zfs_putpage(mapping->host, pp, wbc);
} else {
current->flags |= PF_MEMALLOC;
(void) zfs_putpage(mapping->host, pp, wbc);
current->flags &= ~PF_MEMALLOC;
}
return (0);
}