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authorDavid Howells <dhowells@redhat.com>2022-03-11 15:58:21 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-11 10:24:37 -0800
commit173ce1ca47c489135b2799f70f550e1319ba36d8 (patch)
tree5dc9f1cd8aeb26aed6e552d93831c881312df016 /fs/afs
parent4edc0760412b0c4ecefc7e02cb855b310b122825 (diff)
afs: Fix potential thrashing in afs writeback
In afs_writepages_region(), if the dirty page we find is undergoing writeback or write to cache, but the sync_mode is WB_SYNC_NONE, we go round the loop trying the same page again and again with no pausing or waiting unless and until another thread manages to clear the writeback and fscache flags. Fix this with three measures: (1) Advance start to after the page we found. (2) Break out of the loop and return if rescheduling is requested. (3) Arbitrarily give up after a maximum of 5 skips. Fixes: 31143d5d515e ("AFS: implement basic file write support") Reported-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Marc Dionne <marc.dionne@auristor.com> Acked-by: Marc Dionne <marc.dionne@auristor.com> Link: https://lore.kernel.org/r/164692725757.2097000.2060513769492301854.stgit@warthog.procyon.org.uk/ # v1 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/afs')
-rw-r--r--fs/afs/write.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 5e9157d0da29..f447c902318d 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -703,7 +703,7 @@ static int afs_writepages_region(struct address_space *mapping,
struct folio *folio;
struct page *head_page;
ssize_t ret;
- int n;
+ int n, skips = 0;
_enter("%llx,%llx,", start, end);
@@ -754,8 +754,15 @@ static int afs_writepages_region(struct address_space *mapping,
#ifdef CONFIG_AFS_FSCACHE
folio_wait_fscache(folio);
#endif
+ } else {
+ start += folio_size(folio);
}
folio_put(folio);
+ if (wbc->sync_mode == WB_SYNC_NONE) {
+ if (skips >= 5 || need_resched())
+ break;
+ skips++;
+ }
continue;
}