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ceph: avoid pending truncate during nonblocking cap acquire

PATCH In review Max Kellermann 2 participants 2 messages Sep 4 – Sep 5

Subsystems (2)
Stable branch Ceph client
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Max Kellermann

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#0 lore raw

PATCH 1/1 ceph: avoid pending truncate during nonblocking cap acquire

Readahead acquires caps while the folios are locked. This can deadlock when processing a pending truncate; truncate_pagecache() can then attempt to a folio that is already locked.

Return -EAGAIN instead when NON_BLOCKING is set, causing the readahead to be abandoned.

Fixes 49870056005c ("ceph: convert ceph_readpages to ceph_readahead")
Cc [email protected]
Signed-off-by Max Kellermann <[email protected]>
---
 fs/ceph/caps.c | 4 ++++
 1 file changed, 4 insertions(+)
fs/ceph/caps.c +4 -0
index bcb04c6cb92c..86e195c5fd32 100644
@@ -2889,6 +2889,10 @@ static int try_get_cap_refs(struct inode *inode, int need, int want,
 	}
 
 	/* finish pending truncate */
+	if (ci->i_truncate_pending && (flags & NON_BLOCKING)) {
+		ret = -EAGAIN;
+		goto out_unlock;
+	}
 	while (ci->i_truncate_pending) {
 		spin_unlock(&ci->i_ceph_lock);
 		if (snap_rwsem_locked) {
Signature · 1 line
2.47.3
Reviewed-by on v1 1/1
#1 lore raw

LGTM.

Reviewed-by Xiubo Li <[email protected]>
Quoted 33 lines · Max Kellermann

Readahead acquires caps while the folios are locked. This can deadlock when processing a pending truncate; truncate_pagecache() can then attempt to a folio that is already locked.

Return -EAGAIN instead when NON_BLOCKING is set, causing the readahead to be abandoned.

Fixes 49870056005c ("ceph: convert ceph_readpages to ceph_readahead")
Cc [email protected]
Signed-off-by Max Kellermann <[email protected]>
---
 fs/ceph/caps.c | 4 ++++
 1 file changed, 4 insertions(+)
fs/ceph/caps.c +4 -1
index bcb04c6cb92c..86e195c5fd32 100644
@@ -2889,6 +2889,10 @@ static int try_get_cap_refs(struct inode *inode, int need, int want,
        }
 
        /* finish pending truncate */
+       if (ci->i_truncate_pending && (flags & NON_BLOCKING)) {
+               ret = -EAGAIN;
+               goto out_unlock;
+       }
        while (ci->i_truncate_pending) {
                spin_unlock(&ci->i_ceph_lock);
                if (snap_rwsem_locked) {
--

2.47.3