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Thu, 06 Mar 2025 17:36:00 -0800 (PST) Date: Thu, 6 Mar 2025 20:35:59 -0500 From: Johannes Weiner To: Nhat Pham Cc: akpm@linux-foundation.org, yosryahmed@google.com, yosry.ahmed@linux.dev, chengming.zhou@linux.dev, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] page_io: zswap: do not crash the kernel on decompression failure Message-ID: <20250307013559.GA423735@cmpxchg.org> References: <20250306205011.784787-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250306205011.784787-1-nphamcs@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 549AAC0009 X-Stat-Signature: gosszq7kais1ydid9itmnjdaze7kq4yj X-HE-Tag: 1741311362-67371 X-HE-Meta: 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 z2jRBKsS 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 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: List-Subscribe: List-Unsubscribe: On Thu, Mar 06, 2025 at 12:50:10PM -0800, Nhat Pham wrote: > Currently, we crash the kernel when a decompression failure occurs in > zswap (either because of memory corruption, or a bug in the compression > algorithm). This is overkill. We should only SIGBUS the unfortunate > process asking for the zswap entry on zswap load, and skip the corrupted > entry in zswap writeback. > > See [1] for a recent upstream discussion about this. > > The zswap writeback case is relatively straightforward to fix. For the > zswap_load() case, we change the return behavior: > > * Return 0 on success. > * Return -ENOENT (with the folio locked) if zswap does not own the > swapped out content. > * Return -EIO if zswap owns the swapped out content, but encounters a > decompression failure for some reasons. The folio will be unlocked, > but not be marked up-to-date, which will eventually cause the process > requesting the page to SIGBUS (see the handling of not-up-to-date > folio in do_swap_page() in mm/memory.c), without crashing the kernel. > * Return -EINVAL if we encounter a large folio, as large folio should > not be swapped in while zswap is being used. Similar to the -EIO case, > we also unlock the folio but do not mark it as up-to-date to SIGBUS > the faulting process. > > As a side effect, we require one extra zswap tree traversal in the load > and writeback paths. Quick benchmarking on a kernel build test shows no > performance difference: > > With the new scheme: > real: mean: 125.1s, stdev: 0.12s > user: mean: 3265.23s, stdev: 9.62s > sys: mean: 2156.41s, stdev: 13.98s > > The old scheme: > real: mean: 125.78s, stdev: 0.45s > user: mean: 3287.18s, stdev: 5.95s > sys: mean: 2177.08s, stdev: 26.52s > > [1]: https://lore.kernel.org/all/ZsiLElTykamcYZ6J@casper.infradead.org/ > > Suggested-by: Matthew Wilcox > Suggested-by: Yosry Ahmed > Suggested-by: Johannes Weiner > Signed-off-by: Nhat Pham Acked-by: Johannes Weiner