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DAOS-13938 dfuse: adjust offset in readdir cache entry list #15190

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merged 1 commit into from
Oct 14, 2024
Merged

DAOS-13938 dfuse: adjust offset in readdir cache entry list #15190

merged 1 commit into from
Oct 14, 2024

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johannlombardi
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The dfuse readdir caching feature stats entries returned by dfs readdir that might be legimitely deleted by another process or another node. When this happens, the dfuse code decides to skip the deleted entry, but might leave the readdir entry cache in an inconsistent state causing the following assertion failure in dfuse_dre_drop():
drc->drc_next_offset == expected_offset + 1 || drc->drc_next_offset == READDIR_EOD

This patch fixes the offset in the linked list of cached readdir entries to support skipped entries.

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@johannlombardi
DAOS-13938 dfuse: adjust offset in readdir cache entry list
5cac231 
The dfuse readdir caching feature stats entries returned by
dfs readdir that might be legimitely deleted by another process
or another node. When this happens, the dfuse code decides to
skip the deleted entry, but might leave the readdir entry cache
in an inconsistent state causing the following assertion failure
in dfuse_dre_drop():
drc->drc_next_offset == expected_offset + 1 || drc->drc_next_offset == READDIR_EOD

This patch fixes the offset in the linked list of cached readdir
entries to support skipped entries.

Signed-off-by: Johann Lombardi <johann.lombardi@gmail.com>
@johannlombardi johannlombardi requested review from a team as code owners September 25, 2024 10:19
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Ticket title is 'dFuse process crashes with the following error sporadically on 2.4 branch'
Status is 'Reopened'
Labels: 'GCP,google-cloud-daos'
https://daosio.atlassian.net/browse/DAOS-13938

jolivier23
jolivier23 reviewed Sep 25, 2024
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src/client/dfuse/ops/readdir.c
@@ -759,6 +761,12 @@ dfuse_do_readdir(struct dfuse_info *dfuse_info, fuse_req_t req, struct dfuse_obj
}

if (drc) {
if (oh->doh_rd_nextc != NULL)
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minor nit, any time I have comments, I use braces on if statement and checkpatch never cared. I personally hate the no braces for single line rule style but that is another story.

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I am with you. I will fix once i need to refresh the patch. Probably after @ashleypittman's review.

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I prefer the brevity of no braces for single-line-if statements as they're often simple but I completely agree that if there are comments involved it needs to be clear what code block they belong to.

ashleypittman
ashleypittman reviewed Sep 26, 2024
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This is a complex issue and I need time to come up to speed with the code but it looks exactly the area I'd expect to need updating so I think Johann is on the right track here.

The reproducer for this issue needs two clients, one performing readdir and another modifying the filesystem, the bug relates to a crash in dfuse when performing the readdir request, this will want testing with both ENOENT errors which should be ignored and other errors which should be (probably) propagated to the readdir call.

I'm working through the code and looking at a reproducer and performing a better review of this PR currently.

src/client/dfuse/ops/readdir.c
@@ -759,6 +761,12 @@ dfuse_do_readdir(struct dfuse_info *dfuse_info, fuse_req_t req, struct dfuse_obj
}

if (drc) {
if (oh->doh_rd_nextc != NULL)
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I prefer the brevity of no braces for single-line-if statements as they're often simple but I completely agree that if there are comments involved it needs to be clear what code block they belong to.

ashleypittman
ashleypittman approved these changes Sep 26, 2024
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This looks correct but I'm not sure it's sufficient to solve the problem entirely.

There are two places that dfs_lookup/create_entry are called in this code and we need to handle both ENOENT and other errors from both sites so at the very least significantly more validation is required here.

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let's land, i will fix the other in a different PR.

@johannlombardi johannlombardi merged commit f42e4c5 into master Oct 14, 2024
54 of 55 checks passed
@johannlombardi johannlombardi deleted the jlo/DAOS-13938 branch October 14, 2024 08:43
@mjmac mjmac mentioned this pull request Nov 13, 2024
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@ashleypittman ashleypittman ashleypittman approved these changes

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