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Fix zfs_putpage() lock inversion

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There exists a lock inversions involving the zfs range lock and the
individual page writeback bits which can result in a deadlock.  To
prevent this we must always manipulate the writeback bit while
holding the range lock.  The exact deadlock is as follows:

------ Process A ------        ------ Process B ------
zpl_writepages                 zpl_fallocate
write_cache_pages              zpl_fallocate_common
zpl_putpage                    zfs_space
zfs_putpage (set bit)          zfs_freesp
zfs_range_lock (wait on lock)  zfs_free_range (take lock)
[has not yet initiated I/O,    truncate_inode_pages_range
the bit will not be cleared]   wait_on_page_writeback (wait on bit)

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Richard Yao <richard.yao@clusterhq.com>
Issue #2976
This commit is contained in:
Brian Behlendorf 2014-12-19 12:57:54 -08:00
parent 2d9d57b0fb
commit 74328ee18f
1 changed files with 2 additions and 3 deletions
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5
module/zfs/zfs_vnops.c
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@ -3899,14 +3899,13 @@ zfs_putpage(struct inode *ip, struct page *pp, struct writeback_control *wbc)
}
#endif
rl = zfs_range_lock(zp, pgoff, pglen, RL_WRITER);
set_page_writeback(pp);
unlock_page(pp);
rl = zfs_range_lock(zp, pgoff, pglen, RL_WRITER);
tx = dmu_tx_create(zsb->z_os);
dmu_tx_hold_write(tx, zp->z_id, pgoff, pglen);
dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
zfs_sa_upgrade_txholds(tx, zp);
err = dmu_tx_assign(tx, TXG_NOWAIT);