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dkim=pass header.d=gmail.com header.s=20210112 header.b=ULCMVuis; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf02.hostedemail.com: domain of huangzhaoyang@gmail.com designates 209.85.208.180 as permitted sender) smtp.mailfrom=huangzhaoyang@gmail.com X-Rspam-User: X-Rspamd-Server: rspam08 X-Stat-Signature: scootmbau33do56hwndju6s3i9n1a94m X-HE-Tag: 1665989946-643135 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Oct 17, 2022 at 1:34 PM Zhaoyang Huang wrote: > > On Fri, Oct 14, 2022 at 8:12 PM Matthew Wilcox wrote: > > > > On Fri, Oct 14, 2022 at 01:30:48PM +0800, zhaoyang.huang wrote: > > > From: Zhaoyang Huang > > > > > > Bellowing RCU stall is reported where kswapd traps in a live lock when shrink > > > superblock's inode list. The direct reason is zombie page keeps staying on the > > > xarray's slot and make the check and retry loop permanently. The root cause is unknown yet > > > and supposed could be an xa update without synchronize_rcu etc. I would like to > > > suggest skip this page to break the live lock as a workaround. > > > > No, the underlying bug should be fixed. > > > > > if (!folio || xa_is_value(folio)) > > > return folio; > > > > > > - if (!folio_try_get_rcu(folio)) > > > + if (!folio_try_get_rcu(folio)) { > > > + xas_advance(xas, folio->index + folio_nr_pages(folio) - 1); > > > goto reset; > > > + } > > > > You can't do this anyway. To call folio_nr_pages() and to look at > > folio->index, you must have a refcount on the page, and this is the > > path where we failed to get the refcount. > OK, could I move the xas like below? > > + if (!folio_try_get_rcu(folio)) { > + xas_next_offset(xas); > goto reset; > + } sorry, It seems the above suggestion doesn't break the loop. update it by moving one step and goto retry instead of restarting from ROOT. if (!folio_try_get_rcu(folio)) { xas_next_offset(xas); goto retry; }