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arc: avoid possible deadlock in arc_read

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In l2arc_evict(), the config lock may be acquired in reverse order
(e.g., first the config lock (writer), then a hash lock) unlike in
arc_read() during scenarios like L2ARC device removal. To avoid
deadlocks, if the attempt to acquire the config lock (reader) fails
in arc_read(), release the hash lock, wait for the config lock, and
retry from the beginning.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #17071
This commit is contained in:
Ameer Hamza
2025-02-26 00:32:12 +05:00
committed by GitHub
parent 701093c44f
commit ab3db6d15d
6 changed files with 40 additions and 16 deletions
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module/zfs/arc.c
+22 -4
View File
@@ -5683,6 +5683,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
boolean_t no_buf = *arc_flags & ARC_FLAG_NO_BUF;
arc_buf_t *buf = NULL;
int rc = 0;
boolean_t bp_validation = B_FALSE;
ASSERT(!embedded_bp ||
BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA);
@@ -5725,7 +5726,7 @@ top:
* should always be the case since the blkptr is protected by
* a checksum.
*/
if (!zfs_blkptr_verify(spa, bp, BLK_CONFIG_SKIP,
if (zfs_blkptr_verify(spa, bp, BLK_CONFIG_SKIP,
BLK_VERIFY_LOG)) {
mutex_exit(hash_lock);
rc = SET_ERROR(ECKSUM);
@@ -5877,6 +5878,8 @@ top:
abd_t *hdr_abd;
int alloc_flags = encrypted_read ? ARC_HDR_ALLOC_RDATA : 0;
arc_buf_contents_t type = BP_GET_BUFC_TYPE(bp);
int config_lock;
int error;
if (*arc_flags & ARC_FLAG_CACHED_ONLY) {
if (hash_lock != NULL)
@@ -5885,16 +5888,31 @@ top:
goto done;
}
if (zio_flags & ZIO_FLAG_CONFIG_WRITER) {
config_lock = BLK_CONFIG_HELD;
} else if (hash_lock != NULL) {
/*
* Prevent lock order reversal
*/
config_lock = BLK_CONFIG_NEEDED_TRY;
} else {
config_lock = BLK_CONFIG_NEEDED;
}
/*
* Verify the block pointer contents are reasonable. This
* should always be the case since the blkptr is protected by
* a checksum.
*/
if (!zfs_blkptr_verify(spa, bp,
(zio_flags & ZIO_FLAG_CONFIG_WRITER) ?
BLK_CONFIG_HELD : BLK_CONFIG_NEEDED, BLK_VERIFY_LOG)) {
if (!bp_validation && (error = zfs_blkptr_verify(spa, bp,
config_lock, BLK_VERIFY_LOG))) {
if (hash_lock != NULL)
mutex_exit(hash_lock);
if (error == EBUSY && !zfs_blkptr_verify(spa, bp,
BLK_CONFIG_NEEDED, BLK_VERIFY_LOG)) {
bp_validation = B_TRUE;
goto top;
}
rc = SET_ERROR(ECKSUM);
goto done;
}