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Fix zpl_writepage() deadlock 

Disable the normal reclaim path for zpl_putpage().  This ensures that
all memory allocations under this call path will never enter direct
reclaim.  If this were to happen the VM might try to write out
additional pages by calling zpl_putpage() again resulting in a
deadlock.

This sitution is typically handled in Linux by marking each offending
allocation GFP_NOFS.  However, since much of the code used is common
it makes more sense to use PF_MEMALLOC to flag the entire call tree.
Alternately, the code could be updated to pass the needed allocation
flags but that's a more invasive change.

The following example of the above described deadlock was triggered
by test 074 in the xfstest suite.

Call Trace:
 [<ffffffff814dcdb2>] down_write+0x32/0x40
 [<ffffffffa05af6e4>] dnode_new_blkid+0x94/0x2d0 [zfs]
 [<ffffffffa0597d66>] dbuf_dirty+0x556/0x750 [zfs]
 [<ffffffffa05987d1>] dmu_buf_will_dirty+0x81/0xd0 [zfs]
 [<ffffffffa059ee70>] dmu_write+0x90/0x170 [zfs]
 [<ffffffffa0611afe>] zfs_putpage+0x2ce/0x360 [zfs]
 [<ffffffffa062875e>] zpl_putpage+0x1e/0x60 [zfs]
 [<ffffffffa06287b2>] zpl_writepage+0x12/0x20 [zfs]
 [<ffffffff8115f907>] writeout+0xa7/0xd0
 [<ffffffff8115fa6b>] move_to_new_page+0x13b/0x170
 [<ffffffff8115fed4>] migrate_pages+0x434/0x4c0
 [<ffffffff811559ab>] compact_zone+0x4fb/0x780
 [<ffffffff81155ed1>] compact_zone_order+0xa1/0xe0
 [<ffffffff8115602c>] try_to_compact_pages+0x11c/0x190
 [<ffffffff811200bb>] __alloc_pages_nodemask+0x5eb/0x8b0
 [<ffffffff8115464a>] alloc_pages_current+0xaa/0x110
 [<ffffffff8111e36e>] __get_free_pages+0xe/0x50
 [<ffffffffa03f0e2f>] kv_alloc+0x3f/0xb0 [spl]
 [<ffffffffa03f11d9>] spl_kmem_cache_alloc+0x339/0x660 [spl]
 [<ffffffffa05950b3>] dbuf_create+0x43/0x370 [zfs]
 [<ffffffffa0596fb1>] __dbuf_hold_impl+0x241/0x480 [zfs]
 [<ffffffffa0597276>] dbuf_hold_impl+0x86/0xc0 [zfs]
 [<ffffffffa05977ff>] dbuf_hold_level+0x1f/0x30 [zfs]
 [<ffffffffa05a9dde>] dmu_tx_check_ioerr+0x4e/0x110 [zfs]
 [<ffffffffa05aa1f9>] dmu_tx_count_write+0x359/0x6f0 [zfs]
 [<ffffffffa05aa5df>] dmu_tx_hold_write+0x4f/0x70 [zfs]
 [<ffffffffa0611a6d>] zfs_putpage+0x23d/0x360 [zfs]
 [<ffffffffa062875e>] zpl_putpage+0x1e/0x60 [zfs]
 [<ffffffff811221f9>] write_cache_pages+0x1c9/0x4a0
 [<ffffffffa0628738>] zpl_writepages+0x18/0x20 [zfs]
 [<ffffffff81122521>] do_writepages+0x21/0x40
 [<ffffffff8119bbbd>] writeback_single_inode+0xdd/0x2c0
 [<ffffffff8119bfbe>] writeback_sb_inodes+0xce/0x180
 [<ffffffff8119c11b>] writeback_inodes_wb+0xab/0x1b0
 [<ffffffff8119c4bb>] wb_writeback+0x29b/0x3f0
 [<ffffffff8119c6cb>] wb_do_writeback+0xbb/0x240
 [<ffffffff811308ea>] bdi_forker_task+0x6a/0x310
 [<ffffffff8108ddf6>] kthread+0x96/0xa0

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #327
This commit is contained in:
Brian Behlendorf 2011-07-19 11:48:46 -07:00
parent abd39a8289
commit cfc9a5c88f
1 changed files with 9 additions and 0 deletions
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9
module/zfs/zpl_file.c
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@ -354,7 +354,16 @@ zpl_putpage(struct page *pp, struct writeback_control *wbc, void *data)
{
int error;
/*
* Disable the normal reclaim path for zpl_putpage(). This
* ensures that all memory allocations under this call path
* will never enter direct reclaim. If this were to happen
* the VM might try to write out additional pages by calling
* zpl_putpage() again resulting in a deadlock.
*/
current->flags |= PF_MEMALLOC;
error = -zfs_putpage(pp, wbc, data);
current->flags &= ~PF_MEMALLOC;
if (error) {
SetPageError(pp);