[PATCH 08/10] netfs: Work around recursion by abandoning retry if nothing read

David Howells
2024-12-13T13:51:25Z

syzkaller reported recursion with a loop of three calls (netfs_rreq_assess,
netfs_retry_reads and netfs_rreq_terminated) hitting the limit of the stack
during an unbuffered or direct I/O read.

There are a number of issues:

(1) There is no limit on the number of retries.

(2) A subrequest is supposed to be abandoned if it does not transfer
anything (NETFS_SREQ_NO_PROGRESS), but that isn't checked under all
circumstances.

(3) The actual root cause, which is this:

if (atomic_dec_and_test(&rreq->nr_outstanding))
netfs_rreq_terminated(rreq, ...);

When we do a retry, we bump the rreq->nr_outstanding counter to
prevent the final cleanup phase running before we've finished
dispatching the retries. The problem is if we hit 0, we have to do
the cleanup phase - but we're in the cleanup phase and end up
repeating the retry cycle, hence the recursion.

Work around the problem by limiting the number of retries. This is based
on Lizhi Xu's patch[1], and makes the following changes:

(1) Replace NETFS_SREQ_NO_PROGRESS with NETFS_SREQ_MADE_PROGRESS and make
the filesystem set it if it managed to read or write at least one byte
of data. Clear this bit before issuing a subrequest.

(2) Add a ->retry_count member to the subrequest and increment it any time
we do a retry.

(3) Remove the NETFS_SREQ_RETRYING flag as it is superfluous with
->retry_count. If the latter is non-zero, we're doing a retry.

(4) Abandon a subrequest if retry_count is non-zero and we made no
progress.

(5) Use ->retry_count in both the write-side and the read-size.

[?] Question: Should I set a hard limit on retry_count in both read and
write? Say it hits 50, we always abandon it. The problem is that
these changes only mitigate the issue. As long as it made at least one
byte of progress, the recursion is still an issue. This patch
mitigates the problem, but does not fix the underlying cause. I have
patches that will do that, but it's an intrusive fix that's currently
pending for the next merge window.

The oops generated by KASAN looks something like:

BUG: TASK stack guard page was hit at ffffc9000482ff48 (stack is ffffc90004830000..ffffc90004838000)
Oops: stack guard page: 0000 [#1] PREEMPT SMP KASAN NOPTI
...
RIP: 0010:mark_lock+0x25/0xc60 kernel/locking/lockdep.c:4686
...
mark_usage kernel/locking/lockdep.c:4646 [inline]
__lock_acquire+0x906/0x3ce0 kernel/locking/lockdep.c:5156
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5825
local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
___slab_alloc+0x123/0x1880 mm/slub.c:3695
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3908
__slab_alloc_node mm/slub.c:3961 [inline]
slab_alloc_node mm/slub.c:4122 [inline]
kmem_cache_alloc_noprof+0x2a7/0x2f0 mm/slub.c:4141
radix_tree_node_alloc.constprop.0+0x1e8/0x350 lib/radix-tree.c:253
idr_get_free+0x528/0xa40 lib/radix-tree.c:1506
idr_alloc_u32+0x191/0x2f0 lib/idr.c:46
idr_alloc+0xc1/0x130 lib/idr.c:87
p9_tag_alloc+0x394/0x870 net/9p/client.c:321
p9_client_prepare_req+0x19f/0x4d0 net/9p/client.c:644
p9_client_zc_rpc.constprop.0+0x105/0x880 net/9p/client.c:793
p9_client_read_once+0x443/0x820 net/9p/client.c:1570
p9_client_read+0x13f/0x1b0 net/9p/client.c:1534
v9fs_issue_read+0x115/0x310 fs/9p/vfs_addr.c:74
netfs_retry_read_subrequests fs/netfs/read_retry.c:60 [inline]
netfs_retry_reads+0x153a/0x1d00 fs/netfs/read_retry.c:232
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
...
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_dispatch_unbuffered_reads fs/netfs/direct_read.c:103 [inline]
netfs_unbuffered_read fs/netfs/direct_read.c:127 [inline]
netfs_unbuffered_read_iter_locked+0x12f6/0x19b0 fs/netfs/direct_read.c:221
netfs_unbuffered_read_iter+0xc5/0x100 fs/netfs/direct_read.c:256
v9fs_file_read_iter+0xbf/0x100 fs/9p/vfs_file.c:361
do_iter_readv_writev+0x614/0x7f0 fs/read_write.c:832
vfs_readv+0x4cf/0x890 fs/read_write.c:1025
do_preadv fs/read_write.c:1142 [inline]
__do_sys_preadv fs/read_write.c:1192 [inline]
__se_sys_preadv fs/read_write.c:1187 [inline]
__x64_sys_preadv+0x22d/0x310 fs/read_write.c:1187
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Closes: https://syzkaller.appspot.com/bug?extid=1fc6f64c40a9d143cfb6
Signed-off-by: David Howells <dhowells@redhat.com>
Suggested-by: Lizhi Xu <lizhi.xu@windriver.com>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: v9fs@lists.linux.dev
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20241108034020.3695718-1-lizhi.xu@windriver.com/ [1]
---
fs/9p/vfs_addr.c | 6 +++++-
fs/afs/write.c | 5 ++++-
fs/netfs/read_collect.c | 15 +++++++++------
fs/netfs/read_retry.c | 6 ++++--
fs/netfs/write_collect.c | 5 ++---
fs/netfs/write_issue.c | 2 ++
fs/smb/client/cifssmb.c | 13 +++++++++----
fs/smb/client/smb2pdu.c | 9 ++++++---
include/linux/netfs.h | 6 +++---
9 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 819c75233235..3bc9ce6c575e 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -57,6 +57,8 @@ static void v9fs_issue_write(struct netfs_io_subrequest *subreq)
int err, len;

len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
+ if (len > 0)
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
netfs_write_subrequest_terminated(subreq, len ?: err, false);
}

@@ -80,8 +82,10 @@ static void v9fs_issue_read(struct netfs_io_subrequest *subreq)
if (pos + total >= i_size_read(rreq->inode))
__set_bit(NETFS_SREQ_HIT_EOF, &subreq->flags);

- if (!err)
+ if (!err) {
subreq->transferred += total;
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+ }

netfs_read_subreq_terminated(subreq, err, false);
}
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 34107b55f834..ccb6aa8027c5 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -122,7 +122,7 @@ static void afs_issue_write_worker(struct work_struct *work)
if (subreq->debug_index == 3)
return netfs_write_subrequest_terminated(subreq, -ENOANO, false);

- if (!test_bit(NETFS_SREQ_RETRYING, &subreq->flags)) {
+ if (!subreq->retry_count) {
set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
return netfs_write_subrequest_terminated(subreq, -EAGAIN, false);
}
@@ -149,6 +149,9 @@ static void afs_issue_write_worker(struct work_struct *work)
afs_wait_for_operation(op);
ret = afs_put_operation(op);
switch (ret) {
+ case 0:
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+ break;
case -EACCES:
case -EPERM:
case -ENOKEY:
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index 46ce3b7adf07..47ed3a5044e2 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -438,7 +438,7 @@ void netfs_read_subreq_progress(struct netfs_io_subrequest *subreq,
rreq->origin == NETFS_READPAGE ||
rreq->origin == NETFS_READ_FOR_WRITE)) {
netfs_consume_read_data(subreq, was_async);
- __clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
}
}
EXPORT_SYMBOL(netfs_read_subreq_progress);
@@ -497,7 +497,7 @@ void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq,
rreq->origin == NETFS_READPAGE ||
rreq->origin == NETFS_READ_FOR_WRITE)) {
netfs_consume_read_data(subreq, was_async);
- __clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
}
rreq->transferred += subreq->transferred;
}
@@ -511,10 +511,13 @@ void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq,
} else {
trace_netfs_sreq(subreq, netfs_sreq_trace_short);
if (subreq->transferred > subreq->consumed) {
- __set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
- __clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
- set_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags);
- } else if (!__test_and_set_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags)) {
+ /* If we didn't read new data, abandon retry. */
+ if (subreq->retry_count &&
+ test_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags)) {
+ __set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+ set_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags);
+ }
+ } else if (test_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags)) {
__set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
set_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags);
} else {
diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
index 0350592ea804..0e72e9226fc8 100644
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -56,6 +56,8 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
break;
if (__test_and_clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags)) {
+ __clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+ subreq->retry_count++;
netfs_reset_iter(subreq);
netfs_reissue_read(rreq, subreq);
}
@@ -137,7 +139,8 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
stream0->sreq_max_len = subreq->len;

__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
- __set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
+ __clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+ subreq->retry_count++;

spin_lock_bh(&rreq->lock);
list_add_tail(&subreq->rreq_link, &rreq->subrequests);
@@ -213,7 +216,6 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
subreq->error = -ENOMEM;
__clear_bit(NETFS_SREQ_FAILED, &subreq->flags);
__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
- __clear_bit(NETFS_SREQ_RETRYING, &subreq->flags);
}
spin_lock_bh(&rreq->lock);
list_splice_tail_init(&queue, &rreq->subrequests);
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 82290c92ba7a..ca3a11ed9b54 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -179,7 +179,6 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
struct iov_iter source = subreq->io_iter;

iov_iter_revert(&source, subreq->len - source.count);
- __set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
netfs_reissue_write(stream, subreq, &source);
}
@@ -234,7 +233,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
/* Renegotiate max_len (wsize) */
trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
- __set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
+ subreq->retry_count++;
stream->prepare_write(subreq);

part = min(len, stream->sreq_max_len);
@@ -279,7 +278,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
subreq->start = start;
subreq->debug_index = atomic_inc_return(&wreq->subreq_counter);
subreq->stream_nr = to->stream_nr;
- __set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
+ subreq->retry_count = 1;

trace_netfs_sreq_ref(wreq->debug_id, subreq->debug_index,
refcount_read(&subreq->ref),
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index bf6d507578e5..ff0e82505a0b 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -244,6 +244,8 @@ void netfs_reissue_write(struct netfs_io_stream *stream,
iov_iter_advance(source, size);
iov_iter_truncate(&subreq->io_iter, size);

+ subreq->retry_count++;
+ __clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
netfs_do_issue_write(stream, subreq);
}
diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index bd42a419458e..6cb1e81993f8 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1319,14 +1319,16 @@ cifs_readv_callback(struct mid_q_entry *mid)
}

if (rdata->result == -ENODATA) {
- __set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
rdata->result = 0;
+ __set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
} else {
size_t trans = rdata->subreq.transferred + rdata->got_bytes;
if (trans < rdata->subreq.len &&
rdata->subreq.start + trans == ictx->remote_i_size) {
- __set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
rdata->result = 0;
+ __set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
+ } else if (rdata->got_bytes > 0) {
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &rdata->subreq.flags);
}
}

@@ -1670,10 +1672,13 @@ cifs_writev_callback(struct mid_q_entry *mid)
if (written > wdata->subreq.len)
written &= 0xFFFF;

- if (written < wdata->subreq.len)
+ if (written < wdata->subreq.len) {
result = -ENOSPC;
- else
+ } else {
result = written;
+ if (written > 0)
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &wdata->subreq.flags);
+ }
break;
case MID_REQUEST_SUBMITTED:
case MID_RETRY_NEEDED:
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 010eae9d6c47..458b53d1f9cb 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -4615,6 +4615,7 @@ smb2_readv_callback(struct mid_q_entry *mid)
__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
rdata->result = 0;
}
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &rdata->subreq.flags);
}
trace_smb3_rw_credits(rreq_debug_id, subreq_debug_index, rdata->credits.value,
server->credits, server->in_flight,
@@ -4840,10 +4841,12 @@ smb2_writev_callback(struct mid_q_entry *mid)
if (written > wdata->subreq.len)
written &= 0xFFFF;

- if (written < wdata->subreq.len)
+ if (written < wdata->subreq.len) {
wdata->result = -ENOSPC;
- else
+ } else if (written > 0) {
wdata->subreq.len = written;
+ __set_bit(NETFS_SREQ_MADE_PROGRESS, &wdata->subreq.flags);
+ }
break;
case MID_REQUEST_SUBMITTED:
case MID_RETRY_NEEDED:
@@ -5012,7 +5015,7 @@ smb2_async_writev(struct cifs_io_subrequest *wdata)
}
#endif

- if (test_bit(NETFS_SREQ_RETRYING, &wdata->subreq.flags))
+ if (wdata->subreq.retry_count > 0)
smb2_set_replay(server, &rqst);

cifs_dbg(FYI, "async write at %llu %u bytes iter=%zx\n",
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5eaceef41e6c..4083d77e3f39 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -185,6 +185,7 @@ struct netfs_io_subrequest {
short error; /* 0 or error that occurred */
unsigned short debug_index; /* Index in list (for debugging output) */
unsigned int nr_segs; /* Number of segs in io_iter */
+ u8 retry_count; /* The number of retries (0 on initial pass) */
enum netfs_io_source source; /* Where to read from/write to */
unsigned char stream_nr; /* I/O stream this belongs to */
unsigned char curr_folioq_slot; /* Folio currently being read */
@@ -194,14 +195,13 @@ struct netfs_io_subrequest {
#define NETFS_SREQ_COPY_TO_CACHE 0 /* Set if should copy the data to the cache */
#define NETFS_SREQ_CLEAR_TAIL 1 /* Set if the rest of the read should be cleared */
#define NETFS_SREQ_SEEK_DATA_READ 3 /* Set if ->read() should SEEK_DATA first */
-#define NETFS_SREQ_NO_PROGRESS 4 /* Set if we didn't manage to read any data */
+#define NETFS_SREQ_MADE_PROGRESS 4 /* Set if we transferred at least some data */
#define NETFS_SREQ_ONDEMAND 5 /* Set if it's from on-demand read mode */
#define NETFS_SREQ_BOUNDARY 6 /* Set if ends on hard boundary (eg. ceph object) */
#define NETFS_SREQ_HIT_EOF 7 /* Set if short due to EOF */
#define NETFS_SREQ_IN_PROGRESS 8 /* Unlocked when the subrequest completes */
#define NETFS_SREQ_NEED_RETRY 9 /* Set if the filesystem requests a retry */
-#define NETFS_SREQ_RETRYING 10 /* Set if we're retrying */
-#define NETFS_SREQ_FAILED 11 /* Set if the subreq failed unretryably */
+#define NETFS_SREQ_FAILED 10 /* Set if the subreq failed unretryably */
};

enum netfs_io_origin {