Hi Dan,
We've uncovered another issue during testing with these patches. We get
a kernel panic sometimes just while using a DAX filesystem. I've traced
the issue back to this patch. (There's a stack trace at the end of this
email.)
On 22/09/15 10:42 PM, Dan Williams wrote:
+static void dax_unmap_bh(const struct buffer_head *bh, void __pmem *addr)
+{
+ struct block_device *bdev = bh->b_bdev;
+ struct request_queue *q = bdev->bd_queue;
+
+ if (IS_ERR(addr))
+ return;
+ blk_dax_put(q);
}
@@ -127,9 +159,8 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
if (pos == bh_max) {
bh->b_size = PAGE_ALIGN(end - pos);
bh->b_state = 0;
- retval = get_block(inode, block, bh,
- iov_iter_rw(iter) == WRITE);
- if (retval)
+ rc = get_block(inode, block, bh, rw == WRITE);
+ if (rc)
break;
if (!buffer_size_valid(bh))
bh->b_size = 1 << blkbits;
@@ -178,8 +213,9 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
if (need_wmb)
wmb_pmem();
+ dax_unmap_bh(bh, kmap);
- return (pos == start) ? retval : pos - start;
+ return (pos == start) ? rc : pos - start;
}
The problem is if get_block fails and returns an error code, it will
still call dax_unmap_bh which tries to dereference bh->b_bdev. However,
seeing get_block failed, that pointer is NULL. Maybe a null check in
dax_unmap_bh would be sufficient?
Thanks,
Logan
--
[ 35.391790] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0
[ 35.393306] IP: [<ffffffff811d1731>] dax_unmap_bh+0x41/0x70
[ 35.394253] PGD 7c7ed067 PUD 7c01f067 PMD 0
[ 35.395020] Oops: 0000 [#1] SMP
[ 35.395597] Modules linked in: mtramonb(O)
[ 35.396320] CPU: 0 PID: 1501 Comm: dd Tainted: G O 4.3.0-rc2+ #51
[ 35.397500] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
[ 35.399728] task: ffff88007bc6d600 ti: ffff880079250000 task.ti: ffff880079250000
[ 35.401006] RIP: 0010:[<ffffffff811d1731>] [<ffffffff811d1731>] dax_unmap_bh+0x41/0x70
[ 35.402402] RSP: 0018:ffff880079253ab8 EFLAGS: 00010246
[ 35.403321] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000012
[ 35.404550] RDX: 0000000000000007 RSI: 0000000000000246 RDI: ffffffff8181f630
[ 35.405783] RBP: ffff880079253ac8 R08: 000000000000000a R09: 000000000000fffe
[ 35.407011] R10: ffff88007fc1ad90 R11: 0000000000006abc R12: fffffffffffffffb
[ 35.408237] R13: 000000000038e000 R14: 000000000038e000 R15: 000000000038e000
[ 35.409466] FS: 00007f0e81476700(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
[ 35.410830] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 35.411796] CR2: 00000000000000a0 CR3: 000000007926f000 CR4: 00000000000006f0
[ 35.412990] Stack:
[ 35.413340] 00000000ffffffe4 ffff880079253cf0 ffff880079253be0 ffffffff811d2259
[ 35.414670] 0000000000000246 ffffffff81203120 ffff880079253e68 0000000000000000
[ 35.415981] 000000017c394800 000000000038e000 0000000100000000 fffffffffffffffb
[ 35.417298] Call Trace:
[ 35.417727] [<ffffffff811d2259>] dax_do_io+0x199/0x700
[ 35.418615] [<ffffffff81203120>] ? _ext4_get_block+0x200/0x200
[ 35.419819] [<ffffffff81249700>] ? jbd2_journal_stop+0x60/0x390
[ 35.420886] [<ffffffff8123e7fd>] ext4_ind_direct_IO+0x8d/0x410
[ 35.421908] [<ffffffff8120205a>] ext4_direct_IO+0x2da/0x540
[ 35.422859] [<ffffffff8120887c>] ? ext4_dirty_inode+0x5c/0x70
[ 35.423841] [<ffffffff8113306a>] generic_file_direct_write+0xaa/0x170
[ 35.424931] [<ffffffff811331f2>] __generic_file_write_iter+0xc2/0x1f0
[ 35.426027] [<ffffffff811fcdcb>] ext4_file_write_iter+0x13b/0x420
[ 35.427066] [<ffffffff81084ca2>] ? pick_next_entity+0xb2/0x190
[ 35.428061] [<ffffffff811891f7>] __vfs_write+0xa7/0xf0
[ 35.428940] [<ffffffff81189b59>] vfs_write+0xa9/0x190
[ 35.429810] [<ffffffff81189a94>] ? vfs_read+0x114/0x130
[ 35.430706] [<ffffffff8118a786>] SyS_write+0x46/0xa0
[ 35.431561] [<ffffffff815f742e>] entry_SYSCALL_64_fastpath+0x12/0x71
[ 35.432637] Code: fe 48 c7 c7 4c 63 7e 81 e8 11 ec f5 ff 48 8b 5b 30 48 c7 c7 52 63 7e 81 31 c0 48 89 de e8 fc eb f5 ff 31 c0 48 c7 c7 30 f6 81 81 <48> 8b 9b a0 00 00 00 e8 e7 eb f5 ff 49 81 fc 00 f0 ff ff 77 08
[ 35.437029] RIP [<ffffffff811d1731>] dax_unmap_bh+0x41/0x70
[ 35.438005] RSP <ffff880079253ab8>
[ 35.438608] CR2: 00000000000000a0
[ 35.439194] ---[ end trace 323695b29b46dd96 ]---
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