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ceph: take the inode lock before acquiring cap refs 

Most of the time, we (or the vfs layer) takes the inode_lock and then
acquires caps, but ceph_read_iter does the opposite, and that can lead
to a deadlock.

When there are multiple clients treading over the same data, we can end
up in a situation where a reader takes caps and then tries to acquire
the inode_lock. Another task holds the inode_lock and issues a request
to the MDS which needs to revoke the caps, but that can't happen until
the inode_lock is unwedged.

Fix this by having ceph_read_iter take the inode_lock earlier, before
attempting to acquire caps.

Fixes: 321fe13c93 ("ceph: add buffered/direct exclusionary locking for reads and writes")
Link: https://tracker.ceph.com/issues/36348
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Jeff Layton 2019-11-13 09:10:27 -05:00 committed by Ilya Dryomov
parent 31f4f5b495
commit a81bc3102b
1 changed files with 18 additions and 7 deletions
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25
fs/ceph/file.c
View File

@ -1264,14 +1264,24 @@ again:
dout("aio_read %p %llx.%llx %llu~%u trying to get caps on %p\n",
inode, ceph_vinop(inode), iocb->ki_pos, (unsigned)len, inode);
if (iocb->ki_flags & IOCB_DIRECT)
ceph_start_io_direct(inode);
else
ceph_start_io_read(inode);
if (fi->fmode & CEPH_FILE_MODE_LAZY)
want = CEPH_CAP_FILE_CACHE | CEPH_CAP_FILE_LAZYIO;
else
want = CEPH_CAP_FILE_CACHE;
ret = ceph_get_caps(filp, CEPH_CAP_FILE_RD, want, -1,
&got, &pinned_page);
if (ret < 0)
if (ret < 0) {
if (iocb->ki_flags & IOCB_DIRECT)
ceph_end_io_direct(inode);
else
ceph_end_io_read(inode);
return ret;
}
if ((got & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0 ||
(iocb->ki_flags & IOCB_DIRECT) ||
@ -1283,16 +1293,12 @@ again:
if (ci->i_inline_version == CEPH_INLINE_NONE) {
if (!retry_op && (iocb->ki_flags & IOCB_DIRECT)) {
ceph_start_io_direct(inode);
ret = ceph_direct_read_write(iocb, to,
NULL, NULL);
ceph_end_io_direct(inode);
if (ret >= 0 && ret < len)
retry_op = CHECK_EOF;
} else {
ceph_start_io_read(inode);
ret = ceph_sync_read(iocb, to, &retry_op);
ceph_end_io_read(inode);
}
} else {
retry_op = READ_INLINE;
@ -1303,11 +1309,10 @@ again:
inode, ceph_vinop(inode), iocb->ki_pos, (unsigned)len,
ceph_cap_string(got));
ceph_add_rw_context(fi, &rw_ctx);
ceph_start_io_read(inode);
ret = generic_file_read_iter(iocb, to);
ceph_end_io_read(inode);
ceph_del_rw_context(fi, &rw_ctx);
}
dout("aio_read %p %llx.%llx dropping cap refs on %s = %d\n",
inode, ceph_vinop(inode), ceph_cap_string(got), (int)ret);
if (pinned_page) {
@ -1315,6 +1320,12 @@ again:
pinned_page = NULL;
}
ceph_put_cap_refs(ci, got);
if (iocb->ki_flags & IOCB_DIRECT)
ceph_end_io_direct(inode);
else
ceph_end_io_read(inode);
if (retry_op > HAVE_RETRIED && ret >= 0) {
int statret;
struct page *page = NULL;